Errors of the Standard Photometric System when Measuring the Brightness of General Illumination Light Sources

The standard photometric system is reviewed, and the reported disagreement between visual observations and photometric measurements of the brightness of colored lights is examined. The causes of these disagreements are failure of the proportionality and additivity assumption, as well as errors in the V(λ) function on which the standard photometric system is based. Alternative systems of heterochromatic photometry are discussed and experimental evidence is presented to demonstrate the need for an improved system of photometry for the comparison of different colored lights.