Specification of Color-Rendering Properties of Fluorescent Lamps

In recent years, increasing attention has been paid to the color-rendering properties of light sources; that is, how objects of various colors appear under them. Prior to the advent of the fluorescent lamp, the measure of the color of a light source also, to a large extent, specified its color-rendering properties. Such lamps were incandescent and as such had spectral energy distributions (SED's) similar to black-body radiators at relatively low color temperatures as modified by any filters which might be used in conjunction therewith. Therefore, the establishment of the color of a light source also established its spectral energy distribution, and thereby the appearance of color under it.

This is not the case with fluorescent lighting. These lamps make possible relatively high levels of illumination of almost any desired color and the large selection of usable phosphors also makes possible considerably different spectral energy distributions for any given color. This latter variable may give rise to a considerable change in the subjective color of an object in going from an area lighted by one type of lamp to one lighted by another. The most common example of this change is found in going from a room lighted by incandescent lamps to one lighted by warm-white fluorescent. It is this obvious change in colors, coupled with the advanced state of development of the sciences of photometry and colorimetry, which has been largely responsible for the increased interest in color-rendition measurements.

The present study was undertaken by the authors as members of a sub-committee on color of the American Standards Association's C-78 committee investigating this subject. The results reported herein are by no means the complete story but merely represent a start in the amassing of the large amount of data which will be necessary for the final solution of this problem. It is hoped that these data will serve to indicate the intricacies of this problem, and serve as a springboard for future investigations.