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What is color rendering index (Ra) in Lighting

The degree to which the light source presents the color of an object is called color rendering. Usually called "color rendering index" (Ra).
Color rendering index (Ra) To LED Lighting-Blog Cover

The color rendering ability of a light source to an object is called color rendering, which is compared with the appearance of the object under the same color temperature or reference light source (incandescent lamp or painting light).

In principle, artificial light should be the same as natural light, so that the human eye can correctly distinguish the color of things. Of course, this depends on the location and purpose of the lighting.

The degree to which the light source presents the color of an object is called color rendering. Usually called “color rendering index” (Ra). Color rendering refers to the relationship between the true color of a thing (its own color) and the color displayed under a certain standard light source. The Ra value is determined by comparing the 8 test colors defined in the DIN6169 standard under the standard light source and the tested light source. The smaller the color difference, the better the color rendering of the tested light source.

A light source with an Ra value of 100 means that the color displayed under its light is consistent with that of a standard light source.

The color rendering index of sunlight is defined as 100, and the color rendering index of incandescent lamps is very close to sunlight, 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 degree of the 8 colors under the test light source and the standard of the same color temperature, to measure the color rendering index of the light source, and take the average deviation value Ra20-100 , 100 is the highest, the greater 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:

90-100 1A Excellent Places where precise color contrast is required

80-89 1B / Places that require correct color judgment

60-79 2 Normal Places requiring medium color rendering

40-59 3 / Places with low requirements for color rendering and small color difference

20-39 4 Poor Places with no specific requirements for color rendering

The theoretical color rendering index of incandescent lamps is 100, but there are many types of incandescent lamps in real life and their applications are different. Therefore, their Ra values are not completely consistent, and can only be said to be close to 100, which is the lamp with 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 lamp 97

Daylight fluorescent lamp 80-94

White fluorescent lamp 75-85

Warm white fluorescent lamp 80-90

Tungsten halogen lamp 95-99

High-pressure mercury lamp 22-51

High pressure sodium lamp 20-30

Metal halide lamp 60-65

Sodium thallium indium lamp 60-65

Dysprosium lamp above 85


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