Luminous intensity measurements of sources using a new detector-based illuminance scale

Abstract

Until recently, the source-based photometric scale of NIST had been derived from the gold-point black-body using a long derivation chain resulting in a scale uncertainty of about 1%. In order to improve the accuracy of the photometric scale, a new detector-based illuminance scale has been realized with an uncertainty about twice as small as that of the previous source-based scale. The realization of the new illuminance scale was made by photometers calibrated for absolute spectral response, traceable to N1ST primary standard detectors using a short derivation chain. The luminous intensity scale is derived from the illuminance scale.With the introduction of the new photometric scale, the photometric calibration services of NIST will include luminous intensity and luminance calibration of different kinds of light sources, measured with standard photometers. Luminous intensity measurements of LEDs are discussed as an example to illustrate the new calibration services. In addition, the new photometric scale will allow calibration of illuminance and luminance meters with standard photometers, using different kinds of light sources.