Color Rendering Index (CIE 1995 Ra)

The Color Rendering Index is a standard for evaluating the spectral fidelity of an illuminant. It is computed by comparing the color rendition of a set of colors to the reference light source, a black body radiator or daylight source, which has a CRI of 100.
A spectral instrument is needed to compute the CRI, and for the value to be completely accurate and the illuminant to be a good light source, the illuminant must be within a certain tolerance of the black body or Daylight color locus, and the CRI Readout will annotate the value with (Caution) if this is not the case. If the color is extremely unlike an illuminant, then the CRI may return Failed. The tolerance dictated by the CIE 1995 standard is 0.0054 Duv from the the Black Body locus for temperatures below 5000ºK, and the Daylight locus above 5000ºK. You may decide to use the CRI values even if they are annotated with (Caution), if you judge the illuminant to be close enough to the illuminant locus to be useful.

CRI95 Options

By default the R9 value will also be shown, which can be useful in judging how lighting renders saturated Reds, as poor Red rendering isn't always evident in the Ra value. An R9 value above 0 is generally considered a minimum requirement for rendering of reds, with a value above 50 being considered good.

You can also turn this extra information off, or choose to display the worst R value from the first 8 test patch colors (the ones used to compute the overall Ra value), or the worst from all 14 CIE 1995 test patch values, or all 14 R values. (You will have to scroll the display to see all of them.)

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