Colour rendering index /CRI
CRI is the abbreviation for color rendering index. It is a so-called photometric quantity which makes the colour rendering of different light sources comparable. The measure does not have a unit.
The CRI value characterizes each light source, how well it can reproduce the colors compared to the sun. The higher the CRI or Ra value, the more natural and pleasant colors are reproduced or perceived.
Typical values are:
- Light bulb up to 100
- Halogen lamp up to 98
- White LEDs 70-95
- Fluorescent lamp 50-90
- High pressure mercury vapor lamp 45-50
- Metal halide lamp 60-95
- Sodium vapor high pressure lamp 18-30
According to DIN 6169, 14 test colours are specified. For these, one measures the secondary spectra with the reference and the test light source. The deviations give 14 reference values (Ri).
To determine the general colour index, the arithmetic mean of the firt eight indices is determined. So add up the eight numbers and divide the result by eight.
The number of reference colours used in the colour rendering index has been increased to 14 and later to 15. The more colours that flow into the calculation of the index, the more accurately it describes the quality of the light.
Since an average of the different Ri values is determined, even a high quality light source may be at loss when playing individual colours.
In our luminaires mainly LEDs with >= CRI 90 are used.