The NIST Detector-Based Luminous Intensity Scale.
The Système International des Unités (SI) base unit for photometry, the candela, has been realized by using absolute detectors rather than absolute sources. This change in method permits luminous intensity calibrations of standard lamps to be carried out with a relative expanded uncertainty (coverage factork= 2, and thus a 2 standard deviation estimate) of 0.46 %, almost a factor-of-two improvement. A group of eight reference photometers has been constructed with silicon photodiodes, matched with filters to mimic the spectral luminous efficiency function for photopic vision. The wide dynamic range of the photometers aid in their calibration. The components of the photometers were carefully measured and selected to reduce the sources of error and to provide baseline data for aging studies. Periodic remeasurement of the photometers indicate that a yearly recalibration is required. The design, characterization, calibration, evaluation, and application of the photometers are discussed.
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
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Cromer
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
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Eppeldauer
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
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Hardis
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
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Larason
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
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Ohno
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
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Parr
calibration; candela; illuminance; lumen; luminous intensity; lux; measurement; photometer; photometry; scale; standards; units