Recent Developments in Detector-Based Photometry and Future Needs in Photometry

In the early history of photometry, sources such as candles, lamps, or blackbodies were always used as standards to realize, maintain and transfer the photometric base unit. Even after the advent of photodetectors in the early twentieth century, lamps have been traditionally used to maintain and transfer the units of luminous intensity and luminous flux. In this case, a group of primary standard lamps is maintained as reference standards, which is transferred to secondary standard lamps, and then further transferred to working standard lamps for routine calibration work. Uncertainties are added at each transfer step in this calibration chain.