Basic concepts in photometry, radiometry, and colorimetry

Authored by: Yoshi Ohno

Handbook of Optoelectronics

Print publication date:  October  2017
Online publication date:  October  2017

Print ISBN: 9781482241785
eBook ISBN: 9781315157009
Adobe ISBN:


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The term photometry refers to measurement of quantities for optical radiation as evaluated according to a standardized human eye response, and therefore, is limited to the visible spectral region (360–830 nm) [1]. Photometry uses either optical radiation detectors constructed to mimic the spectral response of the eye or spectroradiometry coupled with appropriate calculations for weighting by the spectral response of the eye. Typical photometric units include the lumen (luminous flux), the candela (luminous intensity), the lux (illuminance) and the candela per square meter (luminance). On the other hand, measurement of optical radiation at all wavelengths (approximately in the range from 10 nm to 1000 μm including ultraviolet, visible and infrared) is referred to as radiometry. The official definition of radiometry [1] is measurement of the quantities associated with radiant energy. Typical radiometric units include the watt (radiant flux), watt per steradian (radiant intensity), watt per square meter (irradiance) and watt per square meter per steradian (radiance). Radiometry often involves spectrally resolved measurements of these quantities as well as spectrally integrated measurements. Similar to photometry, measurement of color of light sources and objects also deals with broadband measurement of the visible radiation and is referred to as colorimetry. Colorimetry is ascribed to measurement of light spectra weighted by three standardized spectral weighting functions, one of which is identical to the standardized human eye response used in photometry.

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