Color Rendering Index
Color Rendering Index (CRI) is a specification of the color rendering property of a light source.
Description
The CRI is calculated by comparing the colorimetric values for a given set of test colors illuminated by the test light source against the values for the same test colors illuminated by a reference illuminant with a color temperature close to that of the test light source. The calculations produce a rendering index for each patch and the CRI for the light source is the mean of the rendering indices for the test color set. The resulting CRI has a value of 100 if the test light source gives identical rendering indices with the reference illuminant.
The choice of the reference illuminant changes depending on the test light source's color temperature. Below 4000 K a Planckian radiator is used for the reference illuminant. From 4000 K and above a daylight simulated reference illuminant is used.
The basic set of eight test color samples are moderate in saturation, approximately the same in lightness and span the hue circle. An additional six test color samples can be optionally added to the basic eight samples. These six samples vary widely in saturation and lightness, representing four strong primary colors, a flesh tone and a foliage color.
|
CIE 1976 L*a*b* D50, 2° |
||||||
|---|---|---|---|---|---|---|
| Sample | ISCC-NBS Color Name | L* | a* | b* | Approximate Color |
Set |
| 1 | Light grayish red |
62.01
|
18.98
|
12.89
|
|
Basic
|
| 2 | Dark grayish yellow |
61.07
|
2.74
|
29.27
|
|
Basic
|
| 3 | Strong yellow green |
62.16
|
-17.82
|
43.92
|
|
Basic
|
| 4 | Moderate yellowish green |
60.79
|
-31.68
|
15.26
|
|
Basic
|
| 5 | Light bluish green |
61.86
|
-19.06
|
-9.73
|
|
Basic
|
| 6 | Light blue |
60.92
|
-4.03
|
-29.22
|
|
Basic
|
| 7 | Light violet |
61.13
|
17.73
|
-23.87
|
|
Basic
|
| 8 | Light reddish purple |
63.22
|
27.32
|
-12.29
|
|
Basic
|
| 9 | Strong red |
41.87
|
62.01
|
31.81
|
|
Extended
|
| 10 | Strong yellow |
81.97
|
1.81
|
71.59
|
|
Extended
|
| 11 | Strong green |
51.62
|
-41.12
|
11.52
|
|
Extended
|
| 12 | Strong blue |
29.20
|
-5.22
|
-49.38
|
|
Extended
|
| 13 | Light yellowish pink |
80.79
|
13.67
|
21.83
|
|
Extended
|
| 14 | Moderate olive green |
40.81
|
-12.38
|
24.08
|
|
Extended
|
The CRI computed with the basic set is called the General Color Rendering Index.
Reference
CIE 13.2 1974 (Corrected 1988), Method of Measuring and Specifying Colour Rendering Properties of Light Sources.
Updated 15.5.2007
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