The colour rendering index (CRI), sometimes called colour rendition index, is a quantitative measure of the ability of a light source to reveal the colours of various objects faithfully in comparison with an ideal or natural light source. Light sources with a high CRI are desirable in colour-critical applications such as photography and cinematography.
Colour index (Ra) is the standard to evaluate the CRI. Numerically, the highest possible CRI is 100, and the best one is 100 too, at 100Ra, the light is more like nature light. Now, in the lighting industry, usually the CRI is from 60 to 90.
The difference between CRI and CT (Colour Temperature)
1. Colour temperature represents the character of the light source. The CT of the white colour is around 2700K~6500K, CT can represent the colour of the light and the light colour can influence the mood. More detail information can find on Colour Temperature.
2. CRI represents how accurate a lighting source is. The index range is from 0 to 100. It shows the ability of a light source to reveal the real colours of various objects.
3. Because the compose of spectrum in the light is different , so even if two light sources have the same color temperature, the CRI may also be different, that is to say, when you use some warm white light sources, CRI of each of them might not be the same.
4. But CT and CRI are two main features of light source, and are the most important standards to evaluate the light environment.
The CRI of some common light source
Technically, the CRI of incandescent bulb is 100Ra, and it’s the ideal reference light source, can represents the real color of objects correctly. Some common light source’s CRI are as follow:
The classification and the application of CRI
Based on the different application places, International Commission on Illumination (CIE) classified CRI as follow:
CRI and Illuminance decided the visual clarity of the environment. So it’s better to choose the light source with higher CRI and proper illuminance with higher luminance efficiency to have a better visual sense of the environment.
1. If we need to stay in a room in a long time, then the CRI of the light source in that room should at least be 80. The lower CRI is bad for our eyes at that room.
2. At some construction places or factories, if the floor height is above 6m, the CRI can be lower than 80, but should be able to identify the safety colors.
3. For the clothing shop, lighting used here should have a very high CRI, higher than 90 is better.
Some applications of special CRI
1. For lighting source of meat showcase in supermarket and store, the R9 CRI is very important.
2. For lighting source in some Studio, photography studio which need to reveal the real color of the skin, the R15 cannot be very low.
3. For lighting source in museum and art gallery which need to reveal all the colors correctly, the requirements of Ra and R1-R15 are very strict.
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