Invisibility is the state of an object that cannot be seen. An object in this state is said to be invisible. The phenomenon is studied by physics and perceptual psychology.
Alberich puts on the Tarnhelm and vanishes; illustration by Arthur Rackham to Richard Wagner's Das Rheingold
Transparency and translucency
In the field of optics, transparency is the physical property of allowing light to pass through the material without appreciable scattering of light. On a macroscopic scale, the photons can be said to follow Snell's law. Translucency allows light to pass through, but does not necessarily follow Snell's law; the photons can be scattered at either of the two interfaces, or internally, where there is a change in index of refraction. In other words, a translucent material is made up of components with different indices of refraction. A transparent material is made up of components with a uniform index of refraction. Transparent materials appear clear, with the overall appearance of one color, or any combination leading up to a brilliant spectrum of every color. The opposite property of translucency is opacity. Other categories of visual appearance, related to the perception of regular or diffuse reflection and transmission of light, have been organized under the concept of cesia in an order system with three variables, including transparency, translucency and opacity among the involved aspects.
Dichroic filters are created using optically transparent materials.
Translucency of a material being used to highlight the structure of a mushroom
A laser beam bouncing down an acrylic rod, illustrating the total internal reflection of light in a multimode optical fiber
Experimentally measured record low attenuation of silica core optical fiber. At 1550 nm wavelength attenuation components are determined as follows: Rayleigh scattering loss ~ 0.1200 dB/km, infrared absorption loss ~ 0.0150 dB/km, impurity absorption loss ~ 0.0047 dB/km, waveguide imperfection loss ~ 0.0010 dB/km.
