Color rendering index
The color rendering ability of a light source to an object is called colorability, which is compared with the appearance color of the object under the reference or reference light source (incandescent lamp or drawing light) with the same color temperature. The spectral content of light emission determines the light color of the light source, but the same light color can be composed of many, a few or even only two monochromatic light waves, and the color rendering properties of each color are greatly different. The light source with the same light color will have different spectral composition, and the light source with wider spectral composition is more likely to provide better color rendering quality.
When the light source spectrum has little or no main wave reflected by the object under the reference light source, the color will produce obvious color shift. The greater the color difference, the worse the color rendering of the light source. The color rendering index coefficient (Kau fman) is a general method to define the evaluation of color rendering of light sources.
There are two kinds of color development
Faithful color rendering
It is necessary to use the light source with high color rendering index (RA), whose value is close to 100, and the color rendering property is the best.
Effect rendering
It is necessary to emphasize the specific color and express the beautiful life. We can use the method of adding color to enhance the color rendering effect. Using low color temperature light source can make red more bright; using medium color temperature light source to make blue have cool feeling; using high color temperature light source to irradiate object has cold feeling.
Relationship with chromogenic property
When there is little or no main wave reflected by the object under the reference light source, the color difference will be obvious. The greater the degree of color difference, the worse the color rendering of the light source. The color rendering index coefficient (Kau fman) is still a general 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 lamp is very close to sunlight, so it is regarded as an ideal reference light source. This system uses 8 kinds of standard color samples of medium color to test, compares the deviation degree of the eight colors under the test light source and under the same color temperature benchmark, so as to measure the color rendering index of the light source. The average deviation value ra20-100 is taken as the highest, and the larger the average color difference, the lower the Ra value. Light sources below 20 are generally not suitable for general use.
General application of index (RA) grade coloration
90-1001a excellent places requiring accurate color contrast
80-89 1B / places requiring correct color judgment
2-60 for common use
40-593 / places with low requirements for color rendering and small color difference
20-394 poor, no specific requirements for color rendering
The theoretical color rendering index of incandescent lamp is 100, but in real life, there are many kinds of incandescent lamps, and their applications are also different, so the Ra value is not completely consistent. It can only be said that it is close to 100, which is the best lamp with the color rendering performance. The color rendering index values of specific lamps can be seen in the table below.
Color rendering index ra
Incandescent lamp 97
Fluorescent lamp 80-94
White fluorescent lamp 75-85
Warm white fluorescent lamp 80-90
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 over 85
