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Photometry: Sensing Light Color



Yoshihiro Ohno, Steven W. Brown


This article first addresses the need and importance of photometry and colorimetry for many products in our daily life- light bulbs in homes and offices; TV sets, computer monitors, headlights of cars, traffic lights, etc. Then the concepts of photometry based on the standardized visual response V(l) and of colorimetry based on the CIE color matching functions are introduced. Various SI units for photometry - candela, lumen, and lux - are defined. The importance of accurate measurements of the lumen is addressed in light of energy conservation and, particularly, the Energy Policy Act of 1992. The definition of the candela and NIST realization of these photometric units, as well as efforts to maintain international traceability, are described. Also addressed are present difficulties in industry in measuring large varieties of light source products while only limited NIST standard lamps and calibration services are available. NIST is now concentrating its efforts on broadening the variety and range of calibration artifacts in photometry and colorimetry - e.g., for displays and LEDs - as well as reducing the uncertainty of the photometric base units. Finally, limitations of the V(l) function and future needs for standardization in mesopic vision, response for colored lights, and response to flashing lights are addressed.
Optics and Photonics News
No. 9


candela, colorimetry, display, LED, lumen, photometry, standards, uncertainty, units


Ohno, Y. and Brown, S. (2001), Photometry: Sensing Light Color, Optics and Photonics News (Accessed May 27, 2024)


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Created September 1, 2001, Updated February 17, 2017