- Author
- Cromer, C. L. | Eppeldauer, G. | Hardis, J. E. | Larason, T. C. | Ohno, Y. | Parr, A. C.
- Title
- NIST Detector-Based Luminous Intensity Scale.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Journal
- Journal of Research of the National Institute of Standards and Technology, Vol. 101, No. 2, 109-132, March/April 1996
- Keywords
- luminous intensity | photometers | photometry | standards | lamps
- Identifiers
- candela; illuminance; lumen; lux
- Abstract
- The System International des Unites (SI) base unit for photometry, the candela, has been realized by using absolute detectors rather than absolute sources. This change in method permits liminous intensity calibrations of standard lamps to be carried out with a relative expanded uncertainty (coverage factor kappa = 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 photdiodes, 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.