National Institute of Standards and Technology detector-based photometric scale.

The Système International 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 with an expanded uncertainty of 0.46%, almost a factor-of-2 improvement. A group of eight reference photometers has been constructed with silicon photodiodes, matched with filters to mimic the Commission Internationale de l'Eclairage spectral luminous efficiency function for photopic vision.The design, characterization, calibration, evaluation, and further application of the photometers are discussed.