The Color Rendering Index (CRI) is a quantitative measure of the ability of a light source to truly display the colors of various objects compared to natural or standard light sources. Defined by The International Commission on Illumination (CIE) as follows:
Color rendering: The effect of a light source on the color appearance of an object by consciously or subconsciously comparing the color appearance under a reference or standard light source.
The color rendering index of a light source does not indicate the apparent color of the light source; this information is given by the correlated color temperature (CCT). CRI is determined by the spectrum of the light source.
The method of calculating CRI is very similar to the visual assessment, but it is done algorithmically after measuring the spectrum of the light source. The color temperature of the light source must first be determined, which can be calculated from spectral measurements. Because the color temperature of the light source must be determined so that we can choose the appropriate daylight spectrum for comparison. The light source in question is then virtually illuminated onto a series of virtual color palettes called test color samples (TCS), and the reflected colors are measured.
As mentioned earlier, the color rendering index is used to measure the appearance of color to the human eye. It represents how faithfully colors are rendered under artificial light sources compared to natural light sources (the sun).
That is, CRI provides a range of values up to 100, where 100 (sunlight) is the best color rendering light quality, and a CRI below 60 indicates very poor color rendering. Higher than 90 means its color rendering is very good.
In general, a light source with a CRI of 80 to 90 is considered good, and a light source with a CRI of more than 90 is excellent. Among the various types of light bulbs on the market, the CRI of LED light bulbs is generally above 90. Combined with its advantages of low energy consumption and good illumination, LED lights are very popular in high CRI light bulbs.