Measurement and Specification of Color Rendition Properties of Light Sources

"Before our knowledge of the effects of artificial light is satisfactory we must solve the problem of the part played by color." This statement is as true today as is was in 1910, almost fifty years ago, when Herbert E. Ives first discussed color measurements of illuminants before this society.

The two methods used in his day to measure color of light sources are essentially the same today, although both are not highly standardized: spectroradiometric, in which the relative intensities of the spectra of various light sources are measured wavelength by wavelength, and colorimetric, in which the color of each source is matched by methods of color mixture.

Colorimetry today is a science on so firm a basis that it is doubtful whether many persons realize how much additional information is needed before color rendition of a light source can be predicted accurately. The purpose of this report is to review some of the basic procedures and information that are available and necessary for this work, and to point out what still is lacking, or available in only a very limited way, and what remains to be done.