For light source products such as white LEDs whose illuminating color is basically "white light", the coordinates can accurately express the apparent color of the light source. But the specific values ​​are difficult to relate to the habitual light color feeling. People often refer to the color of the orange-red color as "warm color", and the more blazing or slightly more blue is called "cold color". Therefore, it is more intuitive to use the color temperature to indicate the light color of the light source.
When the illuminating color of the light source is the same as the color of the black body radiation at a certain temperature, the temperature of the black body is said to be the color temperature T of the light source, and the unit is open (K). For white LEDs, the illuminating color is often not exactly the same as the chromaticity coordinates of the black body (complete radiator) at various temperatures, and thus cannot be expressed by the color temperature. For ease of comparison, the concept of correlated color temperature (CCT) is employed. That is, when the chromaticity of the light source is closest to the chromaticity of the complete radiator at a certain temperature, that is, when the chromaticity difference on the 1960 CIE-UCS chromaticity diagram is the smallest, the temperature of the complete radiator is called the source. Correlated color temperature R1.LEDs used in lighting engineering, especially white LEDs, in addition to color, the more important characteristic is the color of the surrounding object under the illumination of the LED light and whether the color of the object under complete radiation (such as sunlight) Consistent, the so-called color rendering properties.
In 1974, CIE recommended the method of quantitatively evaluating the color rendering of a light source by using the "test color" method. It is to measure the total color displacement of the standard sample under the illumination of the reference light source and the illumination of the light source to be tested. Chromaticity, expressed as a color rendering index value. The CIE specifies the use of a complete radiator or standard illuminant D as a reference source and sets its color rendering index to 100. It also specifies a number of standard color samples for testing.
According to the color difference formed by the above standard color sample under the reference light source and the light source to be tested, the color rendering property of the light source to be tested is evaluated. The color rendering index of a light source for a standard color sample is called the special color rendering index R1.
R1=100-4.6â–³Ei (2-3)
In the formula, ΔEi is the color difference of the standard color sample of the i-th color under the reference light source and the light source to be tested. The average color rendering index of the light source for the first 8 color samples is called the general color rendering index Ra.
There are 14 standard color samples recommended by CIE. The 1-8 numbers are commonly representative tonal samples of medium saturation and medium brightness, and the samples Nos. 9 to 14 include red, yellow, green, blue and other saturated colors, European and American skin colors and leaf green. In 1985, the State formulated the "Light Source Color Evaluation Method" standard and added a color sample of Chinese women's skin color as the fifteenth standard color sample.
Knowing these color rendering indexes actually has a subtle influence on LED lighting equipment, because in some special occasions, such as studios, shopping malls, beauty salons, etc., different lighting will make the skin react to different states, thus affecting customers. The final result of the purchase or shooting.
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