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The Candela and Photometric and Radiometric Measurements



Albert C. Parr


The national measurement system for photometric and radiometric quantities is presently based upon techniques and a measurement chain that make these quantities traceable to a high accuracy cryogenic radiometer. The redefinition of the candela in 1979 provided the opportunity for national measurement laboratories to base their photometric measurements on optical detector technology rather than on the emission from high temperature blackbody optical sources. The ensuing technical developments of the past 20 years, including the significant improvements in cryogenic radiometer performance, have provided the opportunity to place the fundamental maintenance of most photometric and radiometric quantities upon absolute detector based technology as was envisioned by the 1979 redefinition. This paper will review the status of the NIST implementation of the technical changes mandated by the 1979 redefinition of the candela and its effect upon the maintenance and dissemination of optical radiation measurements.
Journal of Research (NIST JRES) -
106 No. 1


laser power, photometry, radiation temperature, radiometric, standards


Parr, A. (2001), The Candela and Photometric and Radiometric Measurements, Journal of Research (NIST JRES), National Institute of Standards and Technology, Gaithersburg, MD (Accessed June 18, 2024)


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Created January 1, 2001, Updated February 17, 2017