What Is the Color Rendering Index?

The color rendering ability of a light source to an object is called color rendering, which is compared with the appearance color of an object under a reference or reference light source (incandescent lamp or painting light) of the same color temperature. The spectral content emitted by the light determines the light color of the light source, but the same light color can be formed by many, a few or even only two monochromatic light waves, and the color rendering of each color is also very different. Light sources with the same light color will have different spectral compositions. Light sources with broader spectral composition are more likely to provide better color rendering quality.

Color rendering index

When the light source spectrum has little or no main wave reflected by the object under the reference light source, the color will have obvious chromatic aberration. The greater the degree of chromatic aberration, the worse the color rendering properties of the light source for that color. The color rendering index coefficient (Kau fman) is still the common method to define the color rendering of light sources.

The color rendering index of sunlight is defined as 100, and the color rendering index of incandescent lamps is very close to that of daylight, so it is regarded as an ideal reference light source. This system uses 8 standard color samples with medium chroma to test, compare the deviation of the 8 colors under the test light source and the same color temperature, to measure the color rendering index of the light source, and take the average deviation value Ra20-100. With 100 being the highest, the larger the average color difference, the lower the Ra value. Light sources below 20 are generally not suitable for general use.

Index (Ra) grade color rendering general application

90100 1A Excellent place where precise color contrast is required

8089 1B / Places requiring accurate color judgment

6079 2 Places that generally require medium color rendering

4059 3 / Places with lower requirements on color rendering and less color difference

2039 4 Poor places without specific requirements for color rendering

The theoretical color rendering index of incandescent lamps is 100, but there are many types of incandescent lamps in actual life and their applications are different, so their Ra values are not completely the same, it can only be said to be close to 100, which is the best color rendering. The color rendering index values of specific lamps can be seen in the table below.

Light source color rendering index Ra

Incandescent 97

Daylight color fluorescent lamp 8094

White fluorescent lamp 7585

Warm white fluorescent lamp 8090

Tungsten halogen lamp

High pressure mercury lamp 2251

High pressure sodium lamp 20-30

Metal halide lamp 6065

Sodium indium lamp 6065

lights above 85