A researcher whose NIST work with colleagues documents photometric measurement standards and their transfer to instruments and lamps. Photometry weights radiation according to visual response; reproducible measurements therefore require control of source spectrum, geometry and detector response. The calibration procedures make a brightness-related reading comparable between different laboratories.[ref]
NIST Measurement Services: Photometric Calibrations by Yuqin Zong and others. §§3.2–3.5.6: photometric calibration systems, source geometry and correction procedures
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