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Color Measurement

The two scales reviewed here are the Color Rendering Index (CRI) and the Color Quality Scale (CQS).

The CRI was created by the International Commission on Illumination (CIE) in the 1960’s, prior to the
advent of solid state, primarily as a device to compare HID and fluorescent lighting.

The CRI value is a result of comparing the color rendering of a test source illuminating these colors to
that of a perfect source at the same lighting level. It utilizes eight low saturation color samples each
representing a spectral band of visible light and distributed over a range of hues.

Figure 4. Colors of the Color Rendering Index

As a side note, CRI is also subject to correlated color temperature (CCT). For warmer color temperatures
(less than 5000K), the perfect source is a black body radiator (similar to an incandescent bulb). For the
cooler temperatures above 5000K, the perfect source is a specifically defined spectrum of daylight.

There are numerous drawbacks to the CRI, all of which make this scale extremely misleading.

First, the CRI was created in the day of HID and fluorescent. In the forty years since the inception of the
CRI, the competitive nature of the lighting industry has driven endless “tuning” of the phosphors used in
these light sources for the sole purpose of scoring well on the CRI. You can see this in action in the
charts below, where the spikes align with the specific CRI spectral bands. As evidenced by the spectral
distributions of these sources, the CRI is a significant misrepresentation of color rendition.

Figure 5. Laying CRI Over Fluorescent and SSL

Competitive Analysis, Color Rendering in White Light Page 4