Photometer
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A photometer is an instrument for measuring photometric quantities such as luminous flux, illuminance, or luminance.
A photometer
Rumford's photometer
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, wavelength-weighted by the luminosit
Photometer
…A photometer is an instrument for measuring photometric quantities such as luminous flux, illuminance, or luminance. Historically, photometry was done by estimation, comparing the luminous flux of a source with a standard source. By the 19th century…
A lux meter for measuring illuminances in work environments
Illuminance diagram with units and terminology