For white LED and other light-emitting color basically "white" light source, the coordinates can accurately express the apparent color of the light source. But the specific value of the light color is difficult to associate with the habit of feeling together. People often call the light color partial to orange-red is "warm", more blazing white or slightly bluish called "cool", so the use of color temperature to indicate the light source color will be more intuitive.
When the light source is illuminated at the same temperature as the black body radiation at a certain temperature, the temperature of the black body is called the color temperature T of the light source, and the unit is K. For white LED, the light color is often associated with a variety of temperature blackbody (full radiator) color coordinates cannot be exactly the same, then you cannot use color temperature. For ease of comparison, the concept of Correlated Color Temperature (CCT) is used. That is, when the chromaticity of the light source is closest to the chromaticity of the complete radiator at a certain temperature, the chromatic aberration on the 1960CIE-UCS chromaticity diagram is the smallest, then the temperature of the complete radiator is called the light source Correlated color temperature R1.
LED lighting projects, especially the white LED, except to the performance of color, the more important feature is the color of the surrounding objects in the LED light illuminated is the same as the object in complete radiation (such as daylight), called color developing property.
In 1974 CIE recommended the use of "test color"method to quantitatively evaluate the color rendering of the light source, which is to measure the reference light source illumination and under test light source under the standard sample total color shift to be based on the light source to be tested Color, with a color index value to represent. The CIE stipulates that a complete radiator or standard illuminant D is used as a reference light source and a color rendering index is set at 100, and a plurality of standard color swatches for testing are specified.
According to the reference light source and the light source under test, the standard color sample to form the color difference to evaluate the color of the light source color is good or bad. Light source of a standard color of the sample color rendering index called the special color rendering index R1.
△ Ei means that the No. I color sample is the color difference in the reference light source and the color under test light source. The average color rendering index of the light source for the first eight color samples is referred to as the general color rendering index Ra.
CIE recommended standard color samples were 14 species. The sample No. 1-8 is medium saturated, medium brightness representative tone sample, 9th to 14th sample include several saturated color such as red, yellow, green, blue, European and American skin color and the leaf green. In 1985 the state developed a "light source color evaluation method" standard, and increased the color of the Chinese women color samples, as the fifteenth standard color samples.