Photometer

Article By:

Darling, David David Darling Enterprises, Dundee, Angus, Scotland.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.510800

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• Photometer, published June 2014:Download PDF Get Adobe Acrobat Reader

An instrument used to measure the intensity of light or various optical properties of surfaces and substances. Strictly speaking, the term photometer applies only to devices that work in the visible region of the electromagnetic spectrum, at wavelengths from about 360 to 830 nm, and are calibrated so that they respond in the same way as the average human eye. However, the term is also more widely applied to instruments designed for use at infrared and ultraviolet wavelengths or for photon counting. Photometers come in a wide variety of forms to suit different applications (Figs. 1 and 2). Among the optical properties that they may measure are luminous intensity (the unit of which is the candela), luminous flux (measured in lumens), illuminance or luminous flux per unit area (measured in lumens per square meter), luminance or photometric brightness (measured in candelas per square meter), light distribution, light reflectance and transmittance, color, spectral distribution, and visibility. See also: Illuminance; Luminance; Luminous flux; Luminous intensity; Photometry

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