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The International Commission on Illumination (CIE) defines color rendering as the effect of a CRI 90 cold light source on the color appearance of an object compared to a standard medical high contrast cold light source. In other words, CRI is a measurement method for color recognition of medical high contrast cold light sources compared to standard light sources (such as sunlight). CRI is a widely recognized measurement standard and currently the only way to evaluate and report the color rendering of medical high contrast cold light sources. The establishment of CRI as a measurement standard is not far away. Initially, the purpose of developing this standard was to use it to describe the color rendering of fluorescent lamps that were widely used in the 1960s, and to help users understand where fluorescent lamps with linear spectral distribution could be applied.

The comparison based on color perception is also meaningful, provided that the color temperature of the tested medical high contrast cold light source and the reference must be the same. For example, attempting to compare the appearance differences of two identical color samples illuminated by a warm white light source with a color temperature of 2900K and a cool white light source (daylight) with a color temperature of 5600K is a complete waste of time. They must look different. Therefore, the first step is to calculate its correlated color temperature (CCT) based on the measured spectrum. Once this color temperature is achieved, another reference CRI 90 cold light source with the same color temperature can be created mathematically. For the measured light source with a color temperature below 5000K, a blackbody (Planck) radiator should be selected as the reference light source; For the tested medical high color rendering cold light source with a color temperature higher than 5000K, the CIE standard illumination body D is selected based on the high color rendering LED cold light source. Now it is possible to combine the spectrum of the reference high color rendering LED cold light source with each color sample to generate an ideal set of reference color coordinate points (referred to as color points). The same applies to the CRI 90 cold light source being tested. In the color chart, the farther the color points under the high color rendering cold light source are from their corresponding ideal positions, the worse the color rendering and the lower the CRI value.