1.
Maroon 5
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Maroon 5 is an American pop rock band that originated in Los Angeles, California. The band, which self-released an album called We Like Digging, then signed to Reprise Records and released the album The Fourth World in 1997. After the album garnered a tepid response, the band parted ways with the record label, in 2001, the band changed its image by adding guitarist James Valentine and pursuing a different direction under the name Maroon 5. At this point, Carmichael switched to playing keyboards, which has become his main instrument in the band. After these changes, Maroon 5 signed with a subsidiary of J Records, Octone Records, the albums lead single, Harder to Breathe, received heavy airplay, which helped the album to debut at number six on the Billboard 200 chart. In 2004, the album went platinum and has dubbed the sleeper hit of the millennium. The band won the Grammy Award for Best New Artist in 2005, for the next few years, Maroon 5 toured extensively worldwide in support of Songs About Jane and produced two live recordings, 2004s 1.22.03. Acoustic and 2005s Live – Friday the 13th. In 2006, Dusick officially left Maroon 5 after suffering from serious wrist, the band then recorded their second album, It Wont Be Soon Before Long and released it in May 2007. The album reached number one on the US Billboard 200 chart, in September 2010, Maroon 5 released their third studio album Hands All Over, which was re-released in 2011 to include the single Moves like Jagger featuring Christina Aguilera. While the original version of the album received mixed reviews, Moves like Jagger reached the one position on the Billboard Hot 100. The band released their album, Overexposed, on June 26,2012. All four singles of the album were successful on the Billboard Hot 100, including second single One More Night. Keyboardist PJ Morton became a member of the band in 2012. The addition of PJ Morton meant that for the first time, in 2014, the band signed with Interscope Records and released their fifth studio album, V. Maroon 5 has sold more than 20 million albums and 70 million singles worldwide, Adam Levine was introduced to Ryan Dusick by a mutual friend and guitarist, Adam Salzman. Levine was 15 years old and Dusick was 16, three of the five members of the band started playing together at age 12. The four original members of the band met while attending Brentwood EMH School in Los Angeles, while attending Brentwood EMH School, Adam Levine and Jesse Carmichael joined up with Mickey Madden and Ryan Dusick to form Karas Flowers, a rock band. The name was taken from a girl went to their high school that the band had a collective crush on
2.
Overexposed (album)
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Overexposed is the fourth studio album by the American band Maroon 5, released on June 20,2012, by A&M Octone Records. The band worked with different producers, such as Max Martin, the bands guitarist and Levines usual co-writer James Valentine only has four credits on the album. The accompanying artwork, created by LA artist Young & Sick, is a collage of illustrations seemingly inspired by the likes of Picasso. Its title is an allusion to Levines ubiquity, while its sound is a reflection of how the group wishes to retain the large audience they won once again with Moves Like Jagger. The albums lead single Payphone, featuring rapper Wiz Khalifa, produced by Shellback and Benny Blanco, was released and performed on The Voice on April 16,2012. The song was a success, reaching two on the Billboard Hot 100 chart, as well as on the ARIA Charts, while it topped the UK Singles Chart, Canadian Hot 100. The second single, One More Night, was released on June 19,2012, the song topped the Billboard Hot 100 for nine weeks, becoming their longest Hot 100 reign. All four singles released from Overexposed have reached the Hot 100 top-ten, the album received a mixed reception from music critics. Some praised the album, calling it their strongest effort, but others criticized the direction the band decided to take, additionally, critics and fans alike perceived the album as overly focused on Levine. It debuted at number 2 on the UK Albums Chart, selling 38,000 copies, to promote the album, the band started the Overexposed Tour, which lasted from 2012 to 2014. In September 2010, the released their third studio album. While preparing the album, the received a phone call from Robert John Mutt Lange, who had heard the band were beginning to write a new record. The album received favorable reviews from music critics and debuted at number two on the US Billboard 200 chart. Valentine further commented, It would be nice to start working on record next year. I think with the last two records, its been a little bit unbalanced, in that we had so much success, in a perfect world wed tour for six months and maybe record for six months, but thats not the way it works. But the whole point is to more music, and if anything you can spend too much time out there. Valentine also said the band has tons of material available, including holdovers including songs from Hands All Over, I think everybodys been pretty busy compiling ideas for the next one, he stated. With technology and the capacity we have on our laptops
3.
Long-exposure photography
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Long-exposure photography captures one element that conventional photography does not, time. The paths of bright moving objects become clearly visible, clouds form broad bands, head and tail lights of cars become bright streaks, stars form trails in the sky and water smooths over. Only bright objects will form visible trails, however, dark objects usually disappear, boats during daytime long exposures will disappear, but will form bright trails from their lights at night. Whereas there is no fixed definition of what constitutes long, the intent is to create a photo that shows the effect of passing time. A 30-minute photo of an object and surrounding cannot be distinguished from a short exposure, hence. Images with exposure times of several minutes also tend to make moving people or dark objects disappear, often adding a serene, when a scene includes both stationary and moving subjects, a slow shutter speed can cause interesting effects, such as light trails. Long exposures are easiest to accomplish in low-light conditions, but can be done in brighter light using neutral density filters or specially designed cameras, when using a dense neutral density filter your cameras auto focus will not be able to function. It is best to compose and focus without the filter, then once you are happy with the composition, switch to manual focus and put the neutral density filter back on. Long-exposure photography is used in a night-time setting, where the lack of light forces longer exposures. Increasing ISO sensitivity allows for shorter exposures, but substantially decreases image quality through reduced dynamic range and higher noise. By leaving the cameras shutter open for a period of time, more light is absorbed. If the camera is stationary for the period of time that the shutter is open. In this technique, a scene is very dark and the photographer or an assistant takes a light source—it can be small penlight—and moves it about in patterns. The light source can be turned off between strokes, often, stationary objects in the scene are illuminated by briefly turning on studio lights, by one or more flashes from a strobe light, or by increasing the aperture. Long exposures can blur moving water so it has mist-like qualities while keeping stationary objects like land, solargraphy is a technique in which a fixed pinhole camera is used to expose photographic paper for an extremely long amount of time. It is most often used to show the path of the Sun across the sky, one example of this is a single six-month exposure taken by photographer Justin Quinnell, showing sun-trails over Clifton Suspension Bridge between 19 December 2007 and 21 June 2008. Part of the Slow light,6 months over Bristol exhibition and this method of solargraphy uses a simple pinhole camera securely fixed in a position which wont be disturbed. Quinnel constructed his camera from an empty drink can with a 0. 25mm aperture, on February 3,2015 a pinhole camera used in a Georgia State University solargraphy art project was blown up by the Atlanta bomb squad
4.
Star trail
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A star trail is a type of photograph that utilizes long-exposure times to capture the apparent motion of stars in the night sky due to the rotation of the Earth. A star trail photograph shows individual stars as streaks across the image, typical exposure times for a star trail range from 15 minutes to several hours, requiring a bulb setting on the camera to open the shutter for a longer period than is normal. Star trails have been used by astronomers to measure the quality of observing locations for major telescopes. Star trail photographs are captured by placing a camera on a tripod, pointing the lens toward the sky, Star trails are considered relatively easy for amateur astrophotographers to create. Photographers generally make these images by using a SLR camera with its lens focus set to infinity, a cable release allows the photographer to hold the shutter open for the desired amount of time. Typical exposure times begin at 15 minutes and can be many hours long, depending on the length of the star trail streaks on the image. Even though star trail pictures are created under low-light conditions, the exposure times allow for fast films, such as ISO200 and ISO400. Wide-apertures, such as f/5.6 and f/4, are recommended for star trails, because exposure times for star trail photographs can be several hours long, camera batteries can be easily depleted. Mechanical cameras that do not require a battery to open and close the shutter have an advantage over more modern film, on these cameras, the Bulb, or B, exposure setting is used to keep the shutter open. Another problem that digital cameras encounter is an increase in detector noise with increasing exposure time, american astronaut Don Pettit recorded star trails with a digital camera from the International Space Station in Earth orbit between April and June,2012. Pettit described his technique as follows, My star trail images are made by taking a time exposure of about 10 to 15 minutes, however, with modern digital cameras,30 seconds is about the longest exposure possible, due to electronic detector noise effectively snowing out the image. To achieve the longer exposures I do what many amateur astronomers do, I take multiple 30-second exposures, then stack them using imaging software, thus producing the longer exposure. Star trail photographs are possible because of the rotation of the Earth on its axis, the apparent motion of the stars is recorded as streaks on the film or detector. For observers in the hemisphere, aiming the camera towards the north creates an image with concentric circular streaks centered on the north celestial pole. For observers located in the hemisphere, this same effect is achieved by aiming the camera south. In this case, the streaks are centered on the celestial pole. Aiming the camera towards the east or west creates straight-line streaks that are angled with respect to the horizon, the size of the angle depends on the photographers latitude. Star trail photographs can be used by astronomers to determine the quality of a location for telescope observations, Star trail observations of Polaris have been used to measure the quality of seeing in the atmosphere, and the vibrations in telescope mounting systems
5.
Celestial pole
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The north and south celestial poles are the two imaginary points in the sky where the Earths axis of rotation, indefinitely extended, intersects the celestial sphere. The north and south celestial poles appear permanently directly overhead to an observer at the Earths North Pole and South Pole respectively. As the Earth spins on its axis, the two celestial poles remain fixed in the sky, and all other points appear to rotate around them, completing one circuit per day. The celestial poles are also the poles of the equatorial coordinate system, meaning they have declinations of +90 degrees. The celestial poles do not remain permanently fixed against the background of the stars, because of a phenomenon known as the precession of the equinoxes, the poles trace out circles on the celestial sphere, with a period of about 25,700 years. The Earths axis is subject to other complex motions which cause the celestial poles to shift slightly over cycles of varying lengths, see nutation, polar motion. Finally, over long periods the positions of the stars themselves change. An analogous concept applies to other planets, a planets celestial poles are the points in the sky where the projection of the axis of rotation intersects the celestial sphere. These points vary because different planets axes are oriented differently, Celestial bodies other than Earth also have similarly defined celestial poles. The north celestial pole currently is within a degree of the bright star Polaris, Polaris can, of course, only be seen from locations in the northern hemisphere. Polaris is near the pole for only a small fraction of the 25. It will remain a good approximation for about 1,000 years, to find Polaris, face north and locate the Big Dipper and Little Dipper asterisms. Looking at the cup part of the Big Dipper, imagine that the two stars at the edge of the cup form a line pointing upward out of the cup. This line points directly at the star at the tip of the Little Dippers handle and that star is Polaris, the North Star. The south celestial pole is only from the southern hemisphere. It lies in the dim constellation Octans, the Octant, sigma Octantis is identified as the south pole star, over a degree away from the pole, but with a magnitude of 5.5 it is barely visible on a clear night. The south celestial pole can be located from the Southern Cross, draw an imaginary line from γ Crucis to α Crucis—the two stars at the extreme ends of the long axis of the cross—and follow this line through the sky. This point is 5 or 6 degrees from the celestial pole
6.
Paranal Observatory
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By total light-collecting area, it is the largest optical-infrared observatory in the Southern hemisphere, worldwide, it is second to the Mauna Kea Observatory on Hawaii. The Very Large Telescope, the largest telescope on Paranal, is composed of four separate 8.2 m telescopes, in addition, the four main telescopes can combine their light to make a fifth instrument, the Very Large Telescope Interferometer. Four auxiliary telescopes of 1.8 m each are part of the VLTI to make it available when the main telescopes are being used for other projects. The site also houses the 2.6 m VLT Survey Telescope and 4.0 m VISTA survey telescope with wider fields of view for surveying large areas of sky uniformly. From an aerial view of the Paranal Oberservatory, the four units of the VLT with their four small. The Survey Telescope, VST, is adjacent to the VLT. The Very Large Telescope consists of four 8. 2-metre telescopes operating in the visible and these telescopes, along with four smaller auxiliary telescopes, are also combined to operate as an optical interferometer on certain nights of the year. All of the 8. 2-metre telescopes have adaptive optics and a suite of instruments. VISTA is the Visible & Infrared Survey Telescope for Astronomy, a 4. 0-metre telescope with a field of view. It was built close to ESOs VLT by a consortium of 18 universities from the United Kingdom, VISTA was handed over to the European Southern Observatory in December 2009. The VLT Survey Telescope or VST is a 2. 6-metre telescope with a wide field imager intended to aid the four Very Large Telescope in their scientific aims, the Next-Generation Transit Survey is an exoplanet-survey facility located a few kilometers from the main peak. It consists of an array of twelve 0. 2-meter robotic telescopes with a large field of view of 96 square degrees or several hundred times the area of the full moon. The survey aims to discover numerous super-Earths and Neptune-sized planets around nearby stars, NGTS is managed by a partnership of seven academic institutions from Chile, Germany, Switzerland and the United Kingdom and its design is based on the SuperWASP project. Science operations began in early 2015, as well as the telescopes, control buildings and maintenance facilities, Paranal has a Residencia which provides accommodation for staff and visitors. This is located 200 m lower and 3 km from the telescopes and it is built half into the mountain with the concrete coloured to blend into the landscape. It has gym facilities, a pool, a restaurant. The construction was decorated by the Chilean architect Paula Gutiérrez Erlandsen, the VLT hotel, the Residencia, served as a backdrop for part of the 2008 James Bond film Quantum of Solace. The observatorys facilities were used to stage the Pacific Alliances fourth summit in June 2012, on 14 March 2013, Frederik, Crown Prince of Denmark, accompanied by his wife, Princess Mary, visited ESO’s Paranal Observatory, as part of an official visit to Chile
7.
European Southern Observatory
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The European Southern Observatory is a 16-nation intergovernmental research organization for ground-based astronomy. Created in 1962, ESO has provided astronomers with state-of-the-art research facilities, the organisation employs about 730 staff members and receives annual member state contributions of approximately €131 million. Its observatories are located in northern Chile, ESO has built and operated some of the largest and most technologically advanced telescopes. The Atacama Large Millimeter Array observes the universe in the millimetre and submillimetre wavelength ranges and it was completed in March 2013 in an international collaboration by Europe, North America, East Asia and Chile. Currently under construction is the European Extremely Large Telescope and it will use a 39. 3-metre-diameter segmented mirror, and become the worlds largest optical reflecting telescope when operational in 2024. ESOs observing facilities have made discoveries and produced several astronomical catalogues. Its findings include the discovery of the most distant gamma-ray burst, in 2004, the VLT allowed astronomers to obtain the first picture of an extrasolar planet orbiting a brown dwarf 173 light-years away. The idea that European astronomers should establish a large observatory was broached by Walter Baade. It was pursued by Oort, who gathered a group of astronomers in Leiden to consider it on June 21 that year, immediately thereafter, the subject was further discussed at the Groningen conference in the Netherlands. On January 26,1954, an ESO declaration was signed by astronomers from six European countries expressing the wish that a joint European observatory be established in the southern hemisphere. At the time, all reflector telescopes with an aperture of 2 metres or more were located in the northern hemisphere. The decision to build the observatory in the southern hemisphere resulted from the necessity of observing the southern sky, although it was initially planned to set up telescopes in South Africa, tests from 1955 to 1963 demonstrated that a site in the Andes was preferable. On November 15,1963 Chile was chosen as the site for ESOs observatory, the decision was preceded by the ESO Convention, signed 5 October 1962 by Belgium, Germany, France, the Netherlands and Sweden. Otto Heckmann was nominated as the organisations first director general on 1 November 1962, a preliminary proposal for a convention of astronomy organisations in these five countries was drafted in 1954. Although some amendments were made in the document, the convention proceeded slowly until 1960 when it was discussed during that years committee meeting. The new draft was examined in detail, and a member of CERN highlighted the need for a convention between governments. The convention and government involvement became pressing due to rising costs of site-testing expeditions. The final 1962 version was adopted from the CERN convention
8.
Sunset
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Sunset or sundown, is the daily disappearance of the Sun below the horizon as a result of Earths rotation. The Sun will set exactly due west at the equator on the spring and fall equinoxes, the time of sunset is defined in astronomy as the moment when the trailing edge of the Suns disk disappears below the horizon. Dusk is at the end of astronomical twilight, and is the darkest moment of twilight just before night. Sunset creates unique atmospheric conditions such as the intense orange and red colors of the Sun. The time of sunset varies throughout the year, and is determined by the position on Earth, specified by longitude and latitude. During winter and spring, the days get longer and sunsets occur later every day until the day of the latest sunset, in the Northern Hemisphere, the latest sunset occurs late in June or in early July, but not on the summer solstice of June 21. This date depends on the viewers latitude, likewise, the earliest sunset does not occur on the winter solstice, but rather about two weeks earlier, again depending on the viewers latitude. In the Northern Hemisphere, it occurs in early December or late November, for a few weeks surrounding both solstices, both sunrise and sunset get slightly later each day. Even on the equator, sunrise and sunset shift several minutes back and forth through the year and these effects are plotted by an analemma. Sunsets occur almost exactly due west on the equinoxes for all viewers on Earth, exact calculations of the azimuths of sunset on other dates are complex, but they can be estimated with reasonable accuracy by using the analemma. As sunrise and sunset are calculated from the leading and trailing edges of the Sun, respectively, and not the center, the duration of a daytime is slightly longer than nighttime. Further, because the light from the Sun is refracted as it passes through the Earths atmosphere, refraction also affects the apparent shape of the Sun when it is very close to the horizon. It makes things appear higher in the sky than they really are, light from the bottom edge of the Suns disk is refracted more than light from the top, since refraction increases as the angle of elevation decreases. This raises the apparent position of the edge more than the top. Its width is unaltered, so the disk appears wider than it is high, the Sun also appears larger on the horizon, an optical illusion, similar to the moon illusion. Because the shorter wavelength components, such as blue and green, scatter more strongly, the remaining reddened sunlight can then be scattered by cloud droplets and other relatively large particles to light up the horizon red and orange. The removal of the wavelengths of light is due to Rayleigh scattering by air molecules and particles much smaller than the wavelength of visible light. The scattering by cloud droplets and other particles with diameters comparable to or larger than the sunlights wavelengths is due to Mie scattering and is not strongly wavelength-dependent
9.
Shutter speed
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The amount of light that reaches the film or image sensor is proportional to the exposure time. 1/500th of a second will let half as much light in as 1/250th, the cameras shutter speed, the lenss aperture, and the scenes luminance together determine the amount of light that reaches the film or sensor. Exposure value is a quantity that accounts for the shutter speed and this will achieve a good exposure when all the details of the scene are legible on the photograph. Too much light let into the results in an overly pale image while too little light will result in an overly dark image. Multiple combinations of speed and f-number can give the same exposure value. According to exposure value formula, doubling the exposure time doubles the amount of light, for example, f/8 lets 4 times more light into the camera as f/16 does. In addition to its effect on exposure, the speed changes the way movement appears in photographs. Very short shutter speeds can be used to freeze fast-moving subjects, very long shutter speeds are used to intentionally blur a moving subject for effect. Short exposure times are called fast, and long exposure times slow. Adjustments to the aperture need to be compensated by changes of the speed to keep the same exposure. The agreed standards for shutter speeds are, With this scale, camera shutters often include one or two other settings for making very long exposures, B keeps the shutter open as long as the shutter release is held. T keeps the open until the shutter release is pressed again. The ability of the photographer to take images without noticeable blurring by camera movement is an important parameter in the choice of the slowest possible speed for a handheld camera. Through practice and special techniques such as bracing the camera, arms, or body to minimize movement, using a monopod or a tripod. If a shutter speed is too slow for hand holding, a support, usually a tripod. Image stabilization on digital cameras or lenses can often permit the use of shutter speeds 3–4 stops slower, Shutter priority refers to a shooting mode used in cameras. It allows the photographer to choose a shutter speed setting and allow the camera to decide the correct aperture and this is sometimes referred to as Shutter Speed Priority Auto Exposure, or TV mode, S mode on Nikons and most other brands. Shutter speed is one of methods used to control the amount of light recorded by the cameras digital sensor or film
10.
Fort du Salbert
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Fort du Salbert, also known as Fort Lefebvre, was built between 1874 and 1877. It was named after General François Joseph Lefebvre and it forms part of the Séré de Rivières system fortifications in the fortified region of Belfort in northeastern France. It is located at the summit of Salbert hill to the northwest of Belfort, during the early years of the Cold War it briefly served as an air defense coordination center. Fort du Salbert is one of the ring of forts around Belfort. All of the new generation of forts abandoned sheer walls and bastions in favor of low earth-covered mounds to better resist artillery, during the First World War a number of underground galleries were constructed to link the caponiers to the caserne. Fort du Salbert commands an area of ponds surrounding Malsaucy, and controls roads to Lure, Giromagny and its initial construction cost was 2,120,332 francs dor. Initial manning was 460 men,24 non-commissioned officers, and 13 officers, a well and cistern provided water. Armament in 1882 was five 155mm long guns, eight 120mm long guns, a 1900 modernization was to add a Galopin armored twin 155mm gun turret and an armored observation post. The gun turret project was abandoned, along with an addition of a machine gun turret. The main fort never received the extensive concrete cover that was applied to other Séré de Rivières forts, during the quarrying of the forts stone the caves of Cravanche were discovered in 1876. Currently, the fort has lost much of its original due to the creation in 1950 of the Ouvrage G de la D. A. T. that required modernization of the fort. This article incorporates text translated from the corresponding French Wikipedia article as of January 20,2010, fortified region of Belfort Fort de Giromagny, Salberts neighbor to the north Fort du Salbert at Chemins de mémoire Fort du Salbert at Fortiff Séré Fortifications of the Belfort region
11.
Moonlight
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Moonlight is the light that reaches Earth from the Moon, consisting mostly of sunlight, with some starlight and earthlight reflected from those portions of its surface which the Suns light strikes. The intensity of moonlight varies greatly depending on the lunar cycle, when the Moon is nearest to Earth and viewed at high altitude at tropical latitudes, the illuminance can reach 0.32 lux. The full Moon is about 1,000,000 times fainter than the Sun, the color of moonlight, particularly near full Moon, appears bluish to the human eye compared to most artificial light sources. This is because of the Purkinje effect - the light is not actually tinted blue, the Moons albedo is 0.136, meaning only 13. 6% of sunlight incident on the Moon is reflected. Moonlight generally hampers astronomical viewing, so astronomers usually avoid making observations near full Moon and it takes approximately 1.26 seconds for the moonlight to hit the Earths surface. In folklore, moonlight sometimes has a harmful influence, for example, sleeping in the light of a full Moon on certain nights was said to transform a person into a werewolf. The light of the Moon was thought to worsen the symptoms of lunatics, nyctalopia was thought to be caused by sleeping in moonlight in the tropics. Moon blindness is a name for equine recurrent uveitis and it is no longer thought to be caused by moonlight. In the 16th century, moonmilk, a white limestone precipitate found in caves, was thought to be caused by the rays of the moon. Airglow Daylight Diffuse reflection Earthlight Scotobiology Starlight Phases of the Moon at USNO Strange Moonlight at Science@NASA Moonlight Brightness at LunarLight Photography
12.
Photography
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Typically, a lens is used to focus the light reflected or emitted from objects into a real image on the light-sensitive surface inside a camera during a timed exposure. With an electronic sensor, this produces an electrical charge at each pixel. A negative image on film is used to photographically create a positive image on a paper base, known as a print. The word photography was created from the Greek roots φωτός, genitive of φῶς, light and γραφή representation by means of lines or drawing, several people may have coined the same new term from these roots independently. Johann von Maedler, a Berlin astronomer, is credited in a 1932 German history of photography as having used it in an article published on 25 February 1839 in the German newspaper Vossische Zeitung. Both of these claims are now widely reported but apparently neither has ever been confirmed as beyond reasonable doubt. Credit has traditionally given to Sir John Herschel both for coining the word and for introducing it to the public. Photography is the result of combining several technical discoveries, later Greek mathematicians Aristotle and Euclid also independently described a pinhole camera in the 5th and 4th centuries BCE. Daniele Barbaro described a diaphragm in 1566, wilhelm Homberg described how light darkened some chemicals in 1694. The fiction book Giphantie, published in 1760, by French author Tiphaigne de la Roche, the discovery of the camera obscura that provides an image of a scene dates back to ancient China. Leonardo da Vinci mentions natural camera obscura that are formed by dark caves on the edge of a sunlit valley, a hole in the cave wall will act as a pinhole camera and project a laterally reversed, upside down image on a piece of paper. So the birth of photography was primarily concerned with inventing means to capture, renaissance painters used the camera obscura which, in fact, gives the optical rendering in color that dominates Western Art. The camera obscura literally means dark chamber in Latin and it is a box with a hole in it which allows light to go through and create an image onto the piece of paper. Around the year 1800, British inventor Thomas Wedgwood made the first known attempt to capture the image in a camera obscura by means of a light-sensitive substance and he used paper or white leather treated with silver nitrate. The shadow images eventually darkened all over, the first permanent photoetching was an image produced in 1822 by the French inventor Nicéphore Niépce, but it was destroyed in a later attempt to make prints from it. Niépce was successful again in 1825, in 1826 or 1827, he made the View from the Window at Le Gras, the earliest surviving photograph from nature. Because Niépces camera photographs required a long exposure, he sought to greatly improve his bitumen process or replace it with one that was more practical. With an eye to eventual commercial exploitation, the partners opted for total secrecy, Daguerres efforts culminated in what would later be named the daguerreotype process
13.
Illuminance
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In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates the surface, similarly, luminous emittance is the luminous flux per unit area emitted from a surface. Luminous emittance is also known as luminous exitance, in SI derived units these are measured in lux or lumens per square metre. In the CGS system, the unit of illuminance is the phot, the foot-candle is a non-metric unit of illuminance that is used in photography. Illuminance was formerly often called brightness, but this leads to confusion with other uses of the word, brightness should never be used for quantitative description, but only for nonquantitative references to physiological sensations and perceptions of light. In astronomy, the illuminance stars cast on the Earths atmosphere is used as a measure of their brightness, the usual units are apparent magnitudes in the visible band. V-magnitudes can be converted to lux using the formula E v =10 /2.5, where Ev is the illuminance in lux, the reverse conversion is M v = −14.18 −2.5 log . Autodesk Design Academy - Measuring Light Levels
14.
Photographic film
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This article is mainly concerned with still photography film. For motion picture film, please see film stock, photographic film is a strip or sheet of transparent plastic film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast, the emulsion will gradually darken if left exposed to light, but the process is too slow and incomplete to be of any practical use. Instead, a short exposure to the image formed by a camera lens is used to produce only a very slight chemical change. This creates an invisible latent image in the emulsion, which can be developed into a visible photograph. In addition to light, all films are sensitive to ultraviolet, X-rays. Unmodified silver halide crystals are only to the blue part of the visible spectrum. This problem was overcome with the discovery that certain dyes, called sensitizing dyes, first orthochromatic and finally panchromatic films were developed. Panchromatic film renders all colors in shades of gray approximately matching their subjective brightness, by similar techniques special-purpose films can be made sensitive to the infrared region of the spectrum. In black-and-white photographic film there is one layer of silver halide crystals. When the exposed silver halide grains are developed, the silver halide crystals are converted to metallic silver, color film has at least three sensitive layers, incorporating different combinations of sensitizing dyes. Typically the blue-sensitive layer is on top, followed by a filter layer to stop any remaining blue light from affecting the layers below. Next come a green-and-blue sensitive layer, and a sensitive layer. During development, the silver halide crystals are converted to metallic silver. Because the by-products are created in direct proportion to the amount of exposure and development, following development, the silver is converted back to silver halide crystals in the bleach step. It is removed from the film during the process of fixing the image on the film with a solution of ammonium thiosulfate or sodium thiosulfate, fixing leaves behind only the formed color dyes, which combine to make up the colored visible image. Later color films, like Kodacolor II, have as many as 12 emulsion layers, the earliest practical photographic process, the daguerreotype, introduced in 1839, did not use film. The light-sensitive chemicals were formed on the surface of a copper sheet
15.
Image sensor
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An image sensor or imaging sensor is a sensor that detects and conveys the information that constitutes an image. It does so by converting the variable attenuation of light waves into signals, the waves can be light or other electromagnetic radiation. As technology changes, digital imaging tends to replace analog imaging, early analog sensors for visible light were video camera tubes. Currently, used types are semiconductor charge-coupled devices or active pixel sensors in complementary metal–oxide–semiconductor or N-type metal-oxide-semiconductor technologies, analog sensors for invisible radiation tend to involve vacuum tubes of various kinds. Digital sensors include flat panel detectors, today, most digital cameras use a CMOS sensor, because CMOS sensors perform better than CCDs. An example is the fact that they incorporate an integrated circuit, CCD is still in use for cheap low entry cameras, but weak in burst mode. Both types of sensor accomplish the task of capturing light. Each cell of a CCD image sensor is an analog device, when light strikes the chip it is held as a small electrical charge in each photo sensor. This process is repeated until all the lines of pixels have had their charge amplified. A CMOS image sensor has an amplifier for each compared to the few amplifiers of a CCD. Some CMOS imaging sensors also use Back-side illumination to increase the number of photons that hit the photodiode, CMOS sensors can potentially be implemented with fewer components, use less power, and/or provide faster readout than CCD sensors. They are also vulnerable to static electricity discharges. Another approach is to utilize the very fine dimensions available in modern CMOS technology to implement a CCD like structure entirely in CMOS technology and this can be achieved by separating individual poly-silicon gates by a very small gap. These hybrid sensors are still in the phase and can potentially harness the benefits of both CCD and CMOS imagers. There are many parameters that can be used to evaluate the performance of a sensor, including dynamic range, signal-to-noise ratio. For sensors of comparable types, the ratio and dynamic range improve as the size increases. In order to avoid interpolated color information, techniques like color co-site sampling use a mechanism to shift the color sensor in pixel steps. 3CCD, using three discrete image sensors, with the color separation done by a dichroic prism, while in general digital cameras use a flat sensor, Sony prototyped a curved sensor in 2014 to reduce/eliminate Petzval field curvature that occurs with a flat sensor
16.
F-number
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The f-number of an optical system such as a camera lens is the ratio of the systems focal length to the diameter of the entrance pupil. It is a number that is a quantitative measure of lens speed. It is also known as the ratio, f-ratio, f-stop. The f-number is commonly indicated using a hooked f with the format f/N, the f-number N or f# is given by, N = f D where f is the focal length, and D is the diameter of the entrance pupil. It is customary to write f-numbers preceded by f/, which forms a mathematical expression of the pupil diameter in terms of f and N. Ignoring differences in light transmission efficiency, a lens with a greater f-number projects darker images, the brightness of the projected image relative to the brightness of the scene in the lenss field of view decreases with the square of the f-number. Doubling the f-number decreases the brightness by a factor of four. To maintain the same photographic exposure when doubling the f-number, the time would need to be four times as long. Most lenses have a diaphragm, which changes the size of the aperture stop. The entrance pupil diameter is not necessarily equal to the aperture stop diameter, a 100 mm focal length f/4 lens has an entrance pupil diameter of 25 mm. A200 mm focal length f/4 lens has a pupil diameter of 50 mm. The 200 mm lenss entrance pupil has four times the area of the 100 mm lenss entrance pupil, a T-stop is an f-number adjusted to account for light transmission efficiency. The word stop is sometimes confusing due to its multiple meanings, a stop can be a physical object, an opaque part of an optical system that blocks certain rays. In photography, stops are also a used to quantify ratios of light or exposure. The one-stop unit is known as the EV unit. On a camera, the setting is traditionally adjusted in discrete steps. Each stop is marked with its corresponding f-number, and represents a halving of the light intensity from the previous stop. This corresponds to a decrease of the pupil and aperture diameters by a factor of 1/2 or about 0.7071, each element in the sequence is one stop lower than the element to its left, and one stop higher than the element to its right
17.
Luminance
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Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light passes through, is emitted or reflected from a particular area. The SI unit for luminance is candela per square metre, a non-SI term for the same unit is the nit. The CGS unit of luminance is the stilb, which is equal to one candela per square centimetre or 10 kcd/m2, luminance is often used to characterize emission or reflection from flat, diffuse surfaces. The luminance indicates how much power will be detected by an eye looking at the surface from a particular angle of view. Luminance is thus an indicator of how bright the surface will appear, in this case, the solid angle of interest is the solid angle subtended by the eyes pupil. Luminance is used in the industry to characterize the brightness of displays. A typical computer display emits between 50 and 300 cd/m2, the sun has luminance of about 1. 6×109 cd/m2 at noon. Luminance is invariant in geometric optics and this means that for an ideal optical system, the luminance at the output is the same as the input luminance. For real, passive, optical systems, the luminance is at most equal to the input. As an example, if one uses a lens to form an image that is smaller than the source object, the luminous power is concentrated into a smaller area, meaning that the illuminance is higher at the image. The light at the plane, however, fills a larger solid angle so the luminance comes out to be the same assuming there is no loss at the lens. The image can never be brighter than the source, if light travels through a lossless medium, the luminance does not change along a given light ray. In the case of a perfectly diffuse reflector, the luminance is isotropic, then the relationship is simply L v = E v R / π A variety of units have been used for luminance, besides the candela per square metre. One candela per square metre is equal to, 10−4 stilbs π apostilbs π×10−4 lamberts 0.292 foot-lamberts Retinal damage can occur when the eye is exposed to high luminance, damage can occur due to local heating of the retina. Photochemical effects can cause damage, especially at short wavelengths. Also available in PDF form and Google Docs online version Autodesk Design Academy Measuring Light Levels
18.
Lux
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The lux is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is equal to one lumen per square metre, in photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. In English, lux is used as both the singular and plural form, illuminance is a measure of how much luminous flux is spread over a given area. One can think of flux as a measure of the total amount of visible light present. A given amount of light will illuminate a surface more dimly if it is spread over a larger area, however, the same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux. Achieving an illuminance of 500 lux might be possible in a kitchen with a single fluorescent light fixture with an output of 12000 lumens. To light a factory floor with dozens of times the area of the kitchen would require dozens of such fixtures, thus, lighting a larger area to the same level of lux requires a greater number of lumens. As with other SI units, SI prefixes can be used, for instance, a star of apparent magnitude 0 provides 2.08 microlux at the earths surface. A barely perceptible magnitude 6 star provides 8 nanolux, the unobscured sun provides an illumination of up to 100 kilolux on the Earths surface, the exact value depending on time of year and atmospheric conditions. This direct normal illuminance is related to the solar illuminance constant Esc, the illumination provided on a surface by a point source equals the number of lux just described times the cosine of the angle between a ray coming from the source and a normal to the surface. The number of lux falling on the surface equals this cosine times a number that characterizes the source from the point of view in question and it differs from the luminance, which does depend on the angular distribution of the emission. A perfectly white surface with one lux falling on it will emit one lux, like all photometric units, the lux has a corresponding radiometric unit. The weighting factor is known as the luminosity function, the lux is one lumen per square metre, and the corresponding radiometric unit, which measures irradiance, is the watt per square metre. The peak of the luminosity function is at 555 nm, the eyes image-forming visual system is sensitive to light of this wavelength than any other. Other wavelengths of visible light produce fewer lux per watt-per-meter-squared, the luminosity function falls to zero for wavelengths outside the visible spectrum. For a light source with mixed wavelengths, the number of lumens per watt can be calculated by means of the luminosity function and this means that white light sources produce far fewer lumens per watt than the theoretical maximum of 683.002 lm/W. The ratio between the number of lumens per watt and the theoretical maximum is expressed as a percentage known as the luminous efficiency. For example, an incandescent light bulb has a luminous efficiency of only about 2%
19.
Second
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The second is the base unit of time in the International System of Units. It is qualitatively defined as the division of the hour by sixty. SI definition of second is the duration of 9192631770 periods of the corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. Seconds may be measured using a mechanical, electrical or an atomic clock, SI prefixes are combined with the word second to denote subdivisions of the second, e. g. the millisecond, the microsecond, and the nanosecond. Though SI prefixes may also be used to form multiples of the such as kilosecond. The second is also the unit of time in other systems of measurement, the centimetre–gram–second, metre–kilogram–second, metre–tonne–second. Absolute zero implies no movement, and therefore zero external radiation effects, the second thus defined is consistent with the ephemeris second, which was based on astronomical measurements. The realization of the second is described briefly in a special publication from the National Institute of Standards and Technology. 1 international second is equal to, 1⁄60 minute 1⁄3,600 hour 1⁄86,400 day 1⁄31,557,600 Julian year 1⁄, more generally, = 1⁄, the Hellenistic astronomers Hipparchus and Ptolemy subdivided the day into sixty parts. They also used an hour, simple fractions of an hour. No sexagesimal unit of the day was used as an independent unit of time. The modern second is subdivided using decimals - although the third remains in some languages. The earliest clocks to display seconds appeared during the last half of the 16th century, the second became accurately measurable with the development of mechanical clocks keeping mean time, as opposed to the apparent time displayed by sundials. The earliest spring-driven timepiece with a hand which marked seconds is an unsigned clock depicting Orpheus in the Fremersdorf collection. During the 3rd quarter of the 16th century, Taqi al-Din built a clock with marks every 1/5 minute, in 1579, Jost Bürgi built a clock for William of Hesse that marked seconds. In 1581, Tycho Brahe redesigned clocks that displayed minutes at his observatory so they also displayed seconds, however, they were not yet accurate enough for seconds. In 1587, Tycho complained that his four clocks disagreed by plus or minus four seconds, in 1670, London clockmaker William Clement added this seconds pendulum to the original pendulum clock of Christiaan Huygens. From 1670 to 1680, Clement made many improvements to his clock and this clock used an anchor escapement mechanism with a seconds pendulum to display seconds in a small subdial
20.
Exposure value
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In photography, exposure value is a number that represents a combination of a cameras shutter speed and f-number, such that all combinations that yield the same exposure have the same EV. Exposure value is used to indicate an interval on the photographic exposure scale, with a difference of 1 EV corresponding to a standard power-of-2 exposure step. The EV concept was developed by the German shutter manufacturer Friedrich Deckel in the 1950s and its intent was to simplify choosing among equivalent camera exposure settings by replacing combinations of shutter speed and f-number with a single number. This was especially helpful to beginners with limited understanding of the shutter speed and aperture. The concept became known as the Light Value System in Europe, the proper EV was determined by the scene luminance and film speed, it was intended that the system also include adjustment for filters, exposure compensation, and other variables. With all of elements included, the camera would be set by transferring the single number thus determined. Exposure value has been indicated in various ways, although all camera settings with the same EV nominally give the same exposure, they do not necessarily give the same picture. The f-number determines the depth of field, and the shutter speed determines the amount of motion blur, if the EV is known, it can be used to select combinations of exposure time and f-number, as shown in Table 1. Greater exposure values are appropriate for photography in more brightly lit situations, to avoid confusion, some authors have used camera exposure to refer to combinations of camera settings. The 1964 ASA standard for automatic exposure controls for cameras, ASA PH2. 15-1964, took the same approach, common practice among photographers is nonetheless to use “exposure” to refer to camera settings as well as to photometric exposure. If, for example, the f-number is changed, an equivalent exposure time can be determined from t 2 t 1 = N22 N12. Performing this calculation mentally is tedious for most photographers, but the equation is solved with a calculator dial on an exposure meter or a similar dial on a standalone calculator. If the camera controls have detents, constant exposure can be maintained by counting the steps as one control is adjusted, the ratio t/N2 could be used to represent equivalent combinations of exposure time and f-number in a single value. But for many such combinations used in photography, the ratio gives a fractional value with a large denominator. For example, beginning with 1 s and f/1, decreasing exposure gives the simple sequence 0,1,2,3, the last two values shown frequently apply when using ISO100 speed imaging media in outdoor photography. Current cameras do not allow direct setting of EV, and cameras with automatic exposure control generally obviate the need for it, EV can nonetheless be helpful when used to transfer recommended exposure settings from an exposure meter to an exposure calculator. Used as an indicator of camera settings, EV corresponds to actual combinations of shutter speed, when the actual EV matches that recommended by the light level and the ISO speed, these settings should result in the “correct” exposure. If the common value of K =12.5 is used, at EV =15 the luminance is 380 cd/ft2 or 4096 cd/m2
21.
Shutter (photography)
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A shutter can also be used to allow pulses of light to pass outwards, as seen in a movie projector or a signal lamp. A shutter of variable speed is used to control exposure time of the film, the shutter is so constructed that it automatically closes after a certain required time interval. The speed of the shutter is controlled by a ring outside the camera, focal-plane shutters are mounted near the focal plane and move to uncover the film or sensor. Behind-the-lens shutters were used in cameras with limited lens interchangeability. Shutters in front of the lens, sometimes simply a lens cap that is removed and replaced for the long exposures required, were used in the days of photography. Other mechanisms than the aperture and the sliding curtains have been used. The time for which a shutter remains open is determined by a timing mechanism and these were originally pneumatic or clockwork, but since the late twentieth century are mostly electronic. The reciprocal of time in seconds is often used for engraving shutter settings. For example, a marking of 250 denotes 1/250 and this does not cause confusion in practice. The exposure time and the aperture of the lens must together be such as to allow the right amount of light to reach the film or sensor. Additionally, the time must be suitable to handle any motion of the subject. Usually it must be fast enough to freeze rapid motion, unless a controlled degree of motion blur is desired, most shutters have a flash synchronization switch to trigger a flash, if connected. This was quite a complicated matter with mechanical shutters and flashbulbs which took a time to reach full brightness. Special flashbulbs were designed which had a burn, illuminating the scene for the whole time taken by a focal plane shutter slit to move across the film. These problems were solved for non-focal-plane shutters with the advent of electronic flash units which fire virtually instantaneously. When using a focal-plane shutter with a flash, if the shutter is set at its X-sync speed or slower the whole frame will be exposed when the flash fires, some electronic flashes can produce a longer pulse compatible with a focal-plane shutter operated at much higher shutter speeds. The focal-plane shutter will still impart focal-plane shutter distortions to a moving subject. Cinematography uses a rotary shutter in movie cameras, a continuously spinning disc which conceals the image with a reflex mirror during the intermittent motion between frame exposure
22.
Multiple exposure
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The exposure values may or may not be identical to each other. Ordinarily, cameras have a sensitivity to light that is a function of time, for example, a one-second exposure is an exposure in which the camera image is equally responsive to light over the exposure time of one second. The criterion for determining that something is an exposure is that the sensitivity goes up. The simplest example of an exposure is a double exposure without flash. Some single exposures, such as flash and blur use a combination of electronic flash and this effect can be approximated by a Dirac delta measure and a constant finite rectangular window, in combination. For example, a sensitivity window comprising a Dirac comb combined with a pulse, is considered a multiple exposure. In photography and cinematography, multiple exposure is a technique in which the shutter is opened more than once to expose the film multiple times. The resulting image contains the subsequent image/s superimposed over the original, the technique is sometimes used as an artistic visual effect and can be used to create ghostly images or to add people and objects to a scene that were not originally there. It is frequently used in photographic hoaxes and it is considered easiest to have a manual winding camera for double exposures. On automatic winding cameras, as soon as a picture is taken the film is wound to the next frame. Some more advanced automatic winding cameras have the option for multiple exposures, manual winding cameras with a multiple exposure feature can be set to double-expose after making the first exposure. Since shooting multiple exposures will expose the same frame multiple times, for example, to expose the frame twice with correct exposure, a −1 EV compensation have to be done, and −2 EV for exposing four times. This may not be necessary when photographing a lit subject in two different positions against a dark background, as the background area will be essentially unexposed. Medium to low light is ideal for double exposures, a tripod may not be necessary if combining different scenes in one shot. In some conditions, for example, recording the progress of a lunar eclipse in multiple exposures. More than two exposures can be combined, with not to overexpose the film. Digital technology enables images to be superimposed over each other by using a photo editor. These enable the opacity of the images to be altered and for an image to be overlaid over another and they also can set the layers to multiply mode, which adds the colors together rather than making the colors of either image pale and translucent
23.
Film speed
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Film speed is the measure of a photographic films sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system. A closely related ISO system is used to measure the sensitivity of digital imaging systems, highly sensitive films are correspondingly termed fast films. In both digital and film photography, the reduction of exposure corresponding to use of higher sensitivities generally leads to reduced image quality, in short, the higher the sensitivity, the grainier the image will be. Ultimately sensitivity is limited by the efficiency of the film or sensor. The speed of the emulsion was then expressed in degrees Warnerke corresponding with the last number visible on the plate after development. Each number represented an increase of 1/3 in speed, typical speeds were between 10° and 25° Warnerke at the time. The concept, however, was built upon in 1900 by Henry Chapman Jones in the development of his plate tester. In their system, speed numbers were inversely proportional to the exposure required, for example, an emulsion rated at 250 H&D would require ten times the exposure of an emulsion rated at 2500 H&D. The methods to determine the sensitivity were later modified in 1925, the H&D system was officially accepted as a standard in the former Soviet Union from 1928 until September 1951, when it was superseded by GOST 2817-50. The Scheinergrade system was devised by the German astronomer Julius Scheiner in 1894 originally as a method of comparing the speeds of plates used for astronomical photography, Scheiners system rated the speed of a plate by the least exposure to produce a visible darkening upon development. ≈2 The system was extended to cover larger ranges and some of its practical shortcomings were addressed by the Austrian scientist Josef Maria Eder. Scheiners system was abandoned in Germany, when the standardized DIN system was introduced in 1934. In various forms, it continued to be in use in other countries for some time. The DIN system, officially DIN standard 4512 by Deutsches Institut für Normung, was published in January 1934, International Congress of Photography held in Dresden from August 3 to 8,1931. The DIN system was inspired by Scheiners system, but the sensitivities were represented as the base 10 logarithm of the sensitivity multiplied by 10, similar to decibels. Thus an increase of 20° represented an increase in sensitivity. ≈3 /10 As in the Scheiner system, speeds were expressed in degrees, originally the sensitivity was written as a fraction with tenths, where the resultant value 1.8 represented the relative base 10 logarithm of the speed. Tenths were later abandoned with DIN4512, 1957-11, and the example above would be written as 18° DIN, the degree symbol was finally dropped with DIN4512, 1961-10
24.
Photometry (optics)
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Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy in terms of absolute power, in modern photometry, the radiant power at each wavelength is weighted by a luminosity function that models human brightness sensitivity. Typically, this function is the photopic sensitivity function, although the scotopic function or other functions may also be applied in the same way. The human eye is not equally sensitive to all wavelengths of visible light, photometry attempts to account for this by weighing the measured power at each wavelength with a factor that represents how sensitive the eye is at that wavelength. The standardized model of the response to light as a function of wavelength is given by the luminosity function. The eye has different responses as a function of wavelength when it is adapted to light conditions, photopic vision is characteristic of the eyes response at luminance levels over three candela per square metre. Scotopic vision occurs below 2 × 10−5 cd/m2, mesopic vision occurs between these limits and is not well characterised for spectral response. Measurement of the effects of electromagnetic radiation became a field of study as early as the end of 18th century, measurement techniques varied depending on the effects under study and gave rise to different nomenclature. The total heating effect of infrared radiation as measured by thermometers led to development of radiometric units in terms of total energy, use of the human eye as a detector led to photometric units, weighted by the eyes response characteristic. Study of the effects of ultraviolet radiation led to characterization by the total dose or actinometric units expressed in photons per second. Many different units of measure are used for photometric measurements, people sometimes ask why there need to be so many different units, or ask for conversions between units that cant be converted. We are familiar with the idea that the adjective heavy can refer to weight or density, for example, offices are typically brightly illuminated by an array of many recessed fluorescent lights for a combined high luminous flux. A laser pointer has very low luminous flux but is bright in one direction. There are two systems of quantities known as photometric and radiometric quantities. Every quantity in one system has a quantity in the other system. For example, the eye responds much more strongly to light than to red. Watts are units of radiant flux while lumens are units of luminous flux, a comparison of the watt and the lumen illustrates the distinction between radiometric and photometric units. The watt is a unit of power and we are accustomed to thinking of light bulbs in terms of power in watts
25.
Spectrophotometry
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In chemistry, spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses photometers, known as spectrophotometers, that can measure a light intensity as a function of its color. A spectrophotometer is commonly used for the measurement of transmittance or reflectance of solutions, transparent or opaque solids, such as polished glass, or gases. However they can also be designed to measure the diffusivity on any of the listed light ranges that cover around 200 nm -2500 nm using different controls. Within these ranges of light, calibrations are needed on the machine using standards that vary in type depending on the wavelength of the photometric determination, an example of an experiment in which spectrophotometry is used is the determination of the equilibrium constant of a solution. A certain chemical reaction within a solution may occur in a forward, at some point, this chemical reaction will reach a point of balance called an equilibrium point. In order to determine the concentrations of reactants and products at this point. The amount of light passes through the solution is indicative of the concentration of certain chemicals that do not allow light to pass through. The use of spectrophotometers spans various scientific fields, such as physics, materials science, chemistry, biochemistry and they are widely used in many industries including semiconductors, laser and optical manufacturing, printing and forensic examination, as well in laboratories for the study of chemical substances. By 1940 several spectrophotometers were available on the market, but early models could not work in the ultraviolet, arnold O. Beckman developed an improved version at the National Technical Laboratories Company, later the Beckman Instrument Company and ultimately Beckman Coulter. Models A, B, and C were developed, then the model D, all the electronics were contained within the instrument case, and it had a new hydrogen lamp with ultraviolet continuum, and a better monochromator. This instrument was produced from 1941 until 1976 with essentially the same design, nobel chemistry laureate Bruce Merrifield said it was probably the most important instrument ever developed towards the advancement of bioscience. There are two classes of devices, single beam and double beam. A double beam spectrophotometer compares the intensity between two light paths, one path containing a reference sample and the other the test sample. A single-beam spectrophotometer measures the light intensity of the beam before. Although comparison measurements from double-beam instruments are easier and more stable, single-beam instruments can have a dynamic range and are optically simpler. Additionally, some specialized instruments, such as spectrophotometers built onto microscopes or telescopes, are single-beam instruments due to practicality, historically, spectrophotometers use a monochromator containing a diffraction grating to produce the analytical spectrum. The grating can either be movable or fixed, if a single detector, such as a photomultiplier tube or photodiode is used, the grating can be scanned stepwise so that the detector can measure the light intensity at each wavelength
26.
Spectral sensitivity
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Spectral sensitivity is the relative efficiency of detection, of light or other signal, as a function of the frequency or wavelength of the signal. In visual neuroscience, spectral sensitivity is used to describe the different characteristics of the photopigments in the rod cells and cone cells in the retina of the eye. It is known that the rod cells are more suited to scotopic vision and cone cells to photopic vision, and that they differ in their sensitivity to different wavelengths of light. It has been established that the spectral sensitivity of the human eye under daylight conditions is at a wavelength of 555 nm. In photography, film and sensors are often described in terms of their spectral sensitivity, a database of camera spectral sensitivity is created and its space analyzed. For X-ray films, the sensitivity is chosen to be appropriate to the phosphors that respond to X-rays. In sensor systems, where the output is easily quantified, the responsivity can be extended to be wavelength dependent, when the sensor system is linear, its spectral sensitivity and spectral responsivity can both be decomposed with similar basis functions. In some linear applications, the spectral sensitivity may be expressed as a spectral responsivity and it is interesting to contrast the sensitivity of the eye to that of digital camera. The spectral sensitivities of CCD arrays in digital cameras are much narrower for the red, green and this processing is part of what creates the delay between the shutter snap and displaying the picture
27.
Sensitometry
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Sensitometry is the scientific study of light-sensitive materials, especially photographic film. The study has its origins in the work by Ferdinand Hurter and they determined how the density of silver produced varied with the amount of light received, and the method and time of development. Plots of film density versus the log of exposure are called curves, Hurter–Driffield curves, H–D curves, HD curves, H & D curves, D–logE curves. At moderate exposures, the shape is typically a bit like an S slanted so that its base. There is usually a central region of the HD curve which approximates to a line, called the linear or straight-line portion. The low end is called the toe, and at the top, at extremely high exposures, the density may come back down, an effect known as solarisation. Different commercial film materials cover a range from about 0.5 to about 5. Often it is not the film that one views but a second or later generation. In these cases the end-to-end gamma is approximately the product of the separate gammas, photographic paper prints have end-to-end gammas generally somewhat over 1. Projection transparencies for dark surround viewing have end-to-end gamma approximately 1.5, a full set of HD curves for a film shows how these vary with developer type and time. Driffield, being a reprint of their papers, together with a history of their early work
28.
UV filter
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UV filters are individual compounds or mixtures that block or absorb ultraviolet light. UV filters are used in sunscreens to protect skin or in photography to reduce the level of light that strikes the recording medium. UV filters can undergo transformation into less protective or more toxic products. These transformation products can health, historically, photographic films were mostly sensitive to UV light, which caused haziness or fogginess, and in color films a bluish hue. Therefore, as a standard, a UV filter was used, however, newer photographic film and digital cameras are highly insensitive to UV wavelengths. UV filters span the spectrum and are used for a wide variety of applications. Ortho Red ahave negativend Deep Ortho Red lights are used in diffusion transfer, typesetting films/paper. Yellow Gold, Yellow, Lithostar Yellow, and Fuji Yellow filters or safelights provide safe workspaces for contact proofing applications like screen printing and platemaking. Pan Green, Infrared Green, and Dark Green filters or safelights are commonly used in scanning applications, work with panchromatic film, and papers and x-rays. Many photographers and cinematographers still use UV filters as a protection for their lenses glass and coating, due to their low cost, however, UV filters may introduce lens flare and have an adverse impact on contrast and sharpness, especially when a strong light source is present. The correct names for such filters though, are UV pass filter and this is a very specialized area in photography. Excessive UV radiation can expose humans to various risks, including diseases such as sunburns, photo-aging. UV radiation can be classified as UVA, UVB and UVC, ultraviolet absorbing compounds are the main ingredients of sunscreen products and other personal care products. Chemical filters are used in combination in order to get sufficient protection against UV. They protect humans from the effects of UV radiation by absorbing, reflecting or scattering it. The reflection and scattering effecst are done by physical UV filters which are inorganic UV filters such as titaniumdioxide, absorption is accomplished by organic UV filters which are known as chemical UV filters. UV filters are being used due to growing concern about UV radiation and skin cancer. The levels of certain UV-filters in sunscreens vary from 0.5 to 10% and they enter the environment directly through bathing activities in oceans, rivers and lakes or through industrial waste water discharge. Several UV filters have been detected at ppb or ppt levels in surfacewater and wastewater and they are lipophilic and tend to accumulate in the aquatic environment’s soils and sediments as well as in the food chain
29.
Infrared cut-off filter
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Infrared cut-off filters, sometimes called IR filters or heat-absorbing filters, are designed to reflect or block mid-infrared wavelengths while passing visible light. They are often used in devices with bright incandescent light bulbs to prevent unwanted heating, there are also filters which are used in solid state video cameras to block IR due to the high sensitivity of many camera sensors to near-infrared light. These filters typically have a hue to them as they also sometimes block some of the light from the longer red wavelengths. Thus a blue filter makes the picture look blue, a black filter marginally allows more light in the blue wavelength to pass resulting in a slight shift of the color temperature of the photo to a cooler color. Because of this, the term IR filters is used to refer to filters that pass infrared light while completely blocking other wavelengths. However, in applications the term IR filter still can be used as a synonym of infrared cut-off filter. Unlike the eye, sensors based on silicon have sensitivities extending into the near-infrared, such sensors may extend to 1000 nm. Digital cameras are equipped with IR-blocking filters to prevent unnatural-looking images. IR-transmitting filters, or removal of factory IR-blocking filters, are used in infrared photography to pass infrared light and block visible. Such filters appear black to the eye, but are transparent when viewed with an IR sensitive device, such filters can be used both over color camera lenses, and to filter visible light from IR illumination sources. Such filter stock is most easily made available most simply by having any commercial color negative film developed after being exposed to light. The leaders of 35mm film are ideal for this, without wasting an entire roll of film, in the same way, visually opaque black color-positive film emulsions mounted in cardboard, as for routine slide projection, provide inexpensive cardboard-mounted infrared filters. Film sizes larger than 35 mm may be handled in the way for larger filter production. For astrophotography, many photogenic targets are bright in the far red, removal of factory filters increases sensitivity to such targets, and may also increase sharpness, as such filters may also include anti-aliasing filters. UV filter Cold mirror and Hot mirror Interference filter
30.
Infrared photography
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In infrared photography, the film or image sensor used is sensitive to infrared light. The part of the spectrum used is referred to as near-infrared to distinguish it from far-infrared, wavelengths used for photography range from about 700 nm to about 900 nm. Film is usually sensitive to light too, so an infrared-passing filter is used, this lets infrared light pass through to the camera. There is a contribution from chlorophyll fluorescence, but this is marginal and is not the real cause of the brightness seen in infrared photographs. The effect is named after the infrared photography pioneer Robert W. Wood, and not after the material wood, the dark skies, in turn, result in less infrared light in shadows and dark reflections of those skies from water, and clouds will stand out strongly. These wavelengths also penetrate a few millimeters into skin and give a look to portraits. Wood, who discovered the effects that now bear his name. The RPS co-ordinated events to celebrate the centenary of this event in 2010, woods photographs were taken on experimental film that required very long exposures, thus, most of his work focused on landscapes. A further set of infrared landscapes taken by Wood in Italy in 1911 used plates provided for him by CEK Mees at Wratten & Wainwright, Mees also took a few infrared photographs in Portugal in 1910, which are now in the Kodak archives. After 1930, new emulsions from Kodak and other manufacturers became useful to infrared astronomy, Infrared photography became popular with photography enthusiasts in the 1930s when suitable film was introduced commercially. The Times regularly published landscape and aerial photographs taken by their staff photographers using Ilford infrared film, by 193733 kinds of infrared film were available from five manufacturers including Agfa, Kodak and Ilford. False-color infrared photography became widely practiced with the introduction of Kodak Ektachrome Infrared Aero Film, the first version of this, known as Kodacolor Aero-Reversal-Film, was developed by Clark and others at the Kodak for camouflage detection in the 1940s. The film became widely available in 35mm form in the 1960s. The unexpected colors and effects that infrared film can fit well with the psychedelic aesthetic that emerged in the late 1960s. Infrared light lies between the visible and microwave portions of the electromagnetic spectrum, Infrared light has a range of wavelengths, just like visible light has wavelengths that range from red light to violet. Near infrared light is closest in wavelength to visible light and far infrared is closer to the region of the electromagnetic spectrum. The longer, far infrared wavelengths are about the size of a pin head and this requires the use of a tripod to prevent the composition from changing. However, it should be noted that diffraction effects inside a camera are greater at infrared wavelengths so that stopping down the lens too far may actually reduce sharpness
31.
Full-spectrum photography
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Full-spectrum photography is a subset of multispectral imaging, defined among photography enthusiasts as imaging with consumer cameras the full, broad spectrum of a film or camera sensor bandwidth. In practice, specialized broadband/full-spectrum film captures visible and near infrared light, modified digital cameras can detect some ultraviolet, all of the visible and much of the near infrared spectrum, as most digital imaging sensors are sensitive from about 350 nm to 1000 nm. Replacing a hot mirror or infrared blocking filter with a pass or a wide spectrally transmitting filter allows the camera to detect the wider spectrum light at greater sensitivity. A converted full-spectrum camera can be used for photography or infrared photography with the appropriate filters. Uses of full-spectrum photography include fine art photography, geology, forensics & law enforcement, wideband panchromatic film has been available in various forms since the 1920s, when some UV and IR sensitivity remained in commercially available emulsions. The earliest color films sometimes included wider band color than recent commercial photographic emulsions, in the late 1990s enthusiastic photographers began shooting infrared with digital cameras, necessitating either long exposures or the removal of the internal hot mirror. Most replaced the hot mirror with an infrared pass filter of the optical thickness and pass only infrared light to achieve results seen with infrared B&W film. Around 2003, forensics photographers using engineered cameras for specific purposes began modifying off-the-shelf digital cameras to acquire less expensive tools, Full-spectrum photography is used by enthusiasts of ghost hunting, though no claims of actually photographing psychic phenomenon with Full-spectrum or infrared photography have been substantiated. Today, there are a few places that will modify digital cameras to pass broad, a few DSLR cameras such as the Fujifilm FinePix IS Pro are purpose-designed for full spectrum use and respond from approximately 1000 nm to 380 nm. Digital sensors and photographic films can be made to record non-visible ultraviolet, in each case, they generally require special equipment, converted digital cameras, specific filters, highly transmitting lenses, etc. For example, most photographic lenses are made of glass and will filter out most ultraviolet light, instead, expensive lenses made of quartz must be used. Infrared films may be shot in standard cameras using an infrared pass filters, a converted digital camera usually requires that the infrared hot mirror be removed and replaced by a wideband, spectrally flat glass of the same optical path length. Typical glass types used include Schott WG-280 and BK-7, which transmit as much as 90% from around 300 nm to past 1000 nm, removing the hot mirror is tedious and may require special tools and clean rooms. Once the camera is sensitive to the full-spectrum, external filters can be used to selectively filter portions of the UV, visible, another example, using UV/IR filters such as the 18A or U-330 yield a two or three toned image in which blues and yellows dominate. One issue with Full-spectrum photography in either film or digital photography is the chromatic aberration produced by the wideband information. That is, different spectra, including the ultraviolet and infrared, will focus at different focal points, yielding blurry images and color edge effects, there are specialized lenses such as the Nikon 105mm f4.5 UV-Nikkor which are designed to eliminate this chromatic aberration. Little or no shortwave ultraviolet light may be recorded unless selective filtering is applied to cut some or all of the infrared light, the longwave infrared light may also wash out a considerable amount of the visible light in the blue and green areas in a full spectrum photograph. Similarly if infrared light is blocked, the visible light can overwhelm the recording of the ultraviolet light
32.
Radiant energy
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In physics, and in particular as measured by radiometry, radiant energy is the energy of electromagnetic and gravitational radiation. As energy, its SI unit is the joule, the quantity of radiant energy may be calculated by integrating radiant flux with respect to time. The symbol Qe is often used throughout literature to denote radiant energy, in branches of physics other than radiometry, electromagnetic energy is referred to using E or W. The term is used particularly when electromagnetic radiation is emitted by a source into the surrounding environment and this radiation may be visible or invisible to the human eye. The term radiant energy is most commonly used in the fields of radiometry, solar energy, heating and lighting, in modern applications involving transmission of power from one location to another, radiant energy is sometimes used to refer to the electromagnetic waves themselves, rather than their energy. In the past, the term electro-radiant energy has also been used, the term radiant energy also applies to gravitational radiation. For example, the first gravitational waves ever observed were produced by a black hole collision that emitted about 5. 3×1047 joules of gravitational-wave energy. Because electromagnetic radiation can be conceptualized as a stream of photons, alternatively, EM radiation can be viewed as an electromagnetic wave, which carries energy in its oscillating electric and magnetic fields. These two views are completely equivalent and are reconciled to one another in quantum field theory, EM radiation can have various frequencies. The bands of frequency present in a given EM signal may be defined, as is seen in atomic spectra, or may be broad. In the photon picture, the energy carried by each photon is proportional to its frequency, in the wave picture, the energy of a monochromatic wave is proportional to its intensity. This implies that if two EM waves have the intensity, but different frequencies, the one with the higher frequency contains fewer photons. When EM waves are absorbed by an object, the energy of the waves is converted to heat and this is a very familiar effect, since sunlight warms surfaces that it irradiates. Often this phenomenon is associated particularly with infrared radiation, but any kind of radiation will warm an object that absorbs it. EM waves can also be reflected or scattered, in case their energy is redirected or redistributed as well. Radiant energy is one of the mechanisms by which energy can enter or leave an open system, such a system can be man-made, such as a solar energy collector, or natural, such as the Earths atmosphere. In geophysics, most atmospheric gases, including the greenhouse gases, allow the Suns short-wavelength radiant energy to pass through to the Earths surface, heating the ground and oceans. The absorbed solar energy is partly re-emitted as longer wavelength radiation, radiant energy is produced in the sun as a result of nuclear fusion
33.
Joule
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The joule, symbol J, is a derived unit of energy in the International System of Units. It is equal to the transferred to an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre. It is also the energy dissipated as heat when a current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule, one joule can also be defined as, The work required to move an electric charge of one coulomb through an electrical potential difference of one volt, or one coulomb volt. This relationship can be used to define the volt, the work required to produce one watt of power for one second, or one watt second. This relationship can be used to define the watt and this SI unit is named after James Prescott Joule. As with every International System of Units unit named for a person, note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, section 5.2. The CGPM has given the unit of energy the name Joule, the use of newton metres for torque and joules for energy is helpful to avoid misunderstandings and miscommunications. The distinction may be also in the fact that energy is a scalar – the dot product of a vector force. By contrast, torque is a vector – the cross product of a distance vector, torque and energy are related to one another by the equation E = τ θ, where E is energy, τ is torque, and θ is the angle swept. Since radians are dimensionless, it follows that torque and energy have the same dimensions, one joule in everyday life represents approximately, The energy required to lift a medium-size tomato 1 m vertically from the surface of the Earth. The energy released when that same tomato falls back down to the ground, the energy required to accelerate a 1 kg mass at 1 m·s−2 through a 1 m distance in space. The heat required to raise the temperature of 1 g of water by 0.24 °C, the typical energy released as heat by a person at rest every 1/60 s. The kinetic energy of a 50 kg human moving very slowly, the kinetic energy of a 56 g tennis ball moving at 6 m/s. The kinetic energy of an object with mass 1 kg moving at √2 ≈1.4 m/s, the amount of electricity required to light a 1 W LED for 1 s. Since the joule is also a watt-second and the unit for electricity sales to homes is the kW·h. For additional examples, see, Orders of magnitude The zeptojoule is equal to one sextillionth of one joule,160 zeptojoules is equivalent to one electronvolt. The nanojoule is equal to one billionth of one joule, one nanojoule is about 1/160 of the kinetic energy of a flying mosquito
34.
Hertz
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The hertz is the unit of frequency in the International System of Units and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide proof of the existence of electromagnetic waves. Hertz are commonly expressed in SI multiples kilohertz, megahertz, gigahertz, kilo means thousand, mega meaning million, giga meaning billion and tera for trillion. Some of the units most common uses are in the description of waves and musical tones, particularly those used in radio-. It is also used to describe the speeds at which computers, the hertz is equivalent to cycles per second, i. e. 1/second or s −1. In English, hertz is also used as the plural form, as an SI unit, Hz can be prefixed, commonly used multiples are kHz, MHz, GHz and THz. One hertz simply means one cycle per second,100 Hz means one hundred cycles per second, and so on. The unit may be applied to any periodic event—for example, a clock might be said to tick at 1 Hz, the rate of aperiodic or stochastic events occur is expressed in reciprocal second or inverse second in general or, the specific case of radioactive decay, becquerels. Whereas 1 Hz is 1 cycle per second,1 Bq is 1 aperiodic radionuclide event per second, the conversion between a frequency f measured in hertz and an angular velocity ω measured in radians per second is ω =2 π f and f = ω2 π. This SI unit is named after Heinrich Hertz, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, the hertz is named after the German physicist Heinrich Hertz, who made important scientific contributions to the study of electromagnetism. The name was established by the International Electrotechnical Commission in 1930, the term cycles per second was largely replaced by hertz by the 1970s. One hobby magazine, Electronics Illustrated, declared their intention to stick with the traditional kc. Mc. etc. units, sound is a traveling longitudinal wave which is an oscillation of pressure. Humans perceive frequency of waves as pitch. Each musical note corresponds to a frequency which can be measured in hertz. An infants ear is able to perceive frequencies ranging from 20 Hz to 20,000 Hz, the range of ultrasound, infrasound and other physical vibrations such as molecular and atomic vibrations extends from a few femtoHz into the terahertz range and beyond. Electromagnetic radiation is described by its frequency—the number of oscillations of the perpendicular electric and magnetic fields per second—expressed in hertz. Radio frequency radiation is measured in kilohertz, megahertz, or gigahertz
35.
Steradian
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The steradian or square radian is the SI unit of solid angle. It is used in geometry, and is analogous to the radian which quantifies planar angles. The name is derived from the Greek stereos for solid and the Latin radius for ray and it is useful, however, to distinguish between dimensionless quantities of a different nature, so the symbol sr is used to indicate a solid angle. For example, radiant intensity can be measured in watts per steradian, the steradian was formerly an SI supplementary unit, but this category was abolished in 1995 and the steradian is now considered an SI derived unit. A steradian can be defined as the angle subtended at the center of a unit sphere by a unit area on its surface. For a general sphere of radius r, any portion of its surface with area A = r2 subtends one steradian, because the surface area A of a sphere is 4πr2, the definition implies that a sphere measures 4π steradians. By the same argument, the solid angle that can be subtended at any point is 4π sr. Since A = r2, it corresponds to the area of a cap. Therefore one steradian corresponds to the angle of the cross-section of a simple cone subtending the plane angle 2θ, with θ given by, θ = arccos = arccos = arccos ≈0.572 rad. This angle corresponds to the plane angle of 2θ ≈1.144 rad or 65. 54°. A steradian is also equal to the area of a polygon having an angle excess of 1 radian, to 1/4π of a complete sphere. The solid angle of a cone whose cross-section subtends the angle 2θ is, Ω =2 π s r. In two dimensions, an angle is related to the length of the arc that it spans, θ = l r r a d where l is arc length, r is the radius of the circle. For example, a measurement of the width of an object would be given in radians. At the same time its visible area over ones visible field would be given in steradians. Just as the area of a circle is related to its diameter or radius. One-dimensional circular measure has units of radians or degrees, while two-dimensional spherical measure is expressed in steradians, in higher dimensional mathematical spaces, units for analogous solid angles have not been explicitly named. When they are used, they are dealt with by analogy with the circular or spherical cases and that is, as a proportion of the relevant unit hypersphere taken up by the generalized angle, or point set expressed in spherical coordinates
36.
Flux
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Flux is either of two separate simple and ubiquitous concepts throughout physics and applied mathematics. Within a discipline, the term is used consistently. Both concepts have mathematical rigor, enabling comparison of the underlying math when the terminology is unclear, for transport phenomena, flux is a vector quantity, describing the magnitude and direction of the flow of a substance or property. In electromagnetism, flux is a quantity, defined as the surface integral of the component of a vector field perpendicular to the surface at each point. As will be clear, the easiest way to relate the two concepts is that the surface integral of a flux according to the first definition is a flux according to the second definition. The word flux comes from Latin, fluxus means flow, as fluxion, this term was introduced into differential calculus by Isaac Newton. One could argue, based on the work of James Clerk Maxwell, the specific quote from Maxwell is, In the case of fluxes, we have to take the integral, over a surface, of the flux through every element of the surface. The result of operation is called the surface integral of the flux. It represents the quantity which passes through the surface, according to the first definition, flux may be a single vector, or flux may be a vector field / function of position. In the latter case flux can readily be integrated over a surface, by contrast, according to the second definition, flux is the integral over a surface, it makes no sense to integrate a second-definition flux for one would be integrating over a surface twice. Thus, Maxwells quote only makes sense if flux is being used according to the first definition and this is ironic because Maxwell was one of the major developers of what we now call electric flux and magnetic flux according to the second definition. This implies that Maxwell conceived as these fields as flows/fluxes of some sort, given a flux according to the second definition, the corresponding flux density, if that term is used, refers to its derivative along the surface that was integrated. By the Fundamental theorem of calculus, the flux density is a flux according to the first definition. Given a current such as electric current—charge per time, current density would also be a flux according to the first definition—charge per time per area. Concrete fluxes in the rest of this article will be used in accordance to their acceptance in the literature. In transport phenomena, flux is defined as the rate of flow of a property per unit area, the area is of the surface the property is flowing through or across. Here are 3 definitions in increasing order of complexity, each is a special case of the following. In all cases the frequent symbol j, is used for flux, q for the quantity that flows, t for time
37.
Radiosity (radiometry)
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The CGS unit erg per square centimeter per second is often used in astronomy. Radiosity is often called intensity in branches of other than radiometry. For an opaque surface, the component of radiosity Je, tr vanishes. In heat transfer, combining these two factors into one radiosity term helps in determining the net exchange between multiple surfaces. Spectral radiosity in frequency of a surface, denoted Je, ν, is defined as J e, ν = ∂ J e ∂ ν, where ν is the frequency. Spectral radiosity in wavelength of a surface, denoted Je, λ, is defined as J e, λ = ∂ J e ∂ λ, normally, Ee is the unknown variable and will depend on the surrounding surfaces. So, the irradiance of surface i is the sum of energy from all other surfaces per unit surface of area Ai. For an N surface enclosure, this summation for each surface will generate N linear equations with N unknown radiosities, for an enclosure with only a few surfaces, this can be done by hand. But, for a room with many surfaces, linear algebra, once the radiosities have been calculated, the net heat transfer at a surface can be determined by finding the difference between the incoming and outgoing energy, Q ˙ i = A i. For an enclosure consisting of only a few surfaces, it is easier to represent the system with an analogous circuit rather than solve the set of linear radiosity equations. To do this, the transfer at each surface is expressed as Q i ˙ = M e, i ∘ − J e, i R i. Likewise, Me, i° − Je, i is the blackbody exitance minus the radiosity and these quantities are formulated to resemble those from an electrical circuit V = IR. Now performing an analysis for the heat transfer from surface i to surface j, Q ˙ i j = A i F i j = J e, i − J e, j R i j. Because the above is between surfaces, Rij is the resistance of the space between the surfaces and Je, i − Je, j serves as the potential difference, combining the surface elements and space elements, a circuit is formed. The heat transfer is found by using the potential difference and equivalent resistances. In the radiosity method and circuit analogy, several assumptions were made to simplify the model, the most significant is that the surface is a diffuse emitter. In such a case, the radiosity does not depend on the angle of incidence of reflecting radiation, in reality, however, the radiosity will have a specular component from the reflected radiation. So, the transfer between two surfaces relies on both the view factor and the angle of reflected radiation
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