Longterm changes of silicon photodiodes and their use for photometric standardization.

A secondary standard silicon photodiode matched with a V-lambda filter was calibrated against primary standard, self-calibrated inversion layer silicon photodiodes, to achieve a high accuracy photometer, according to the new definition of the canadela (the photometric base unit). The measured several percent/year specular spectral reflectance change of the windowless primary standard photodiodes was eliminated by their repeated self-calibration. This self-calibration also eliminated the measured several tenth of a percent/year spectral response change of the secondary standard silicon photodiode. The secondary standard detector could be a nonunity quantum efficiency light detector. The spectral response calibration of the V-lambda matched detector of medium spectral mismatch (f(1)= 3.0%) against the absolute spectral responses of three self-calibrated photodiodes resulted in a standard deviation of 0.17% in luminous flux (lumen) calibration. Also illuminance (lux) and light intensity (candela) calibrations were derived from the above primary photometric calibration. It is shown that the V-lambda matched photometer with the above spectral calibration can be used for accurate photometric measurements for all kinds of light sources of known spectral power distribution.