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m Hyphenate black-body radiator for internal consistency; add links to pages for "black body" and "black-body radiation" to references that aren't already close to a link to one of those pages |
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==Test method==
The CRI is calculated by comparing the color rendering of the test source to that of a "perfect" source, which is a [[black
{{citation
|title=Color rendering of light sources: CIE method of specification and its application
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===Chromatic adaptation===
[[File:CIE CRI TCS under FL4.svg|thumb|Chromatic adaptation of TCSs lit by CIE FL4 (short, black vectors, to indicate before and after) to a [[black body]] of 2940 K (cyan circles)]]
{{harvtxt|CIE|1995}} uses this von Kries chromatic transform equation to find the [[corresponding color]] (''u''<sub>''c'',''i''</sub>, ''v''<sub>''c'',''i''</sub>) for each sample. The mixed subscripts (''t'', ''i'') refer to the [[inner product]] of the test illuminant spectrum and the spectral reflexivity of sample ''i'':
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* [[#New test color samples|A new set of test color samples]]
* Six reference illuminants: D65, D50, [[black bodies]] of 4200 K, 3450 K, 2950 K, and 2700 K.
* A new chromatic adaptation transform: CIECAT94.
* Color difference evaluation in CIELAB.
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<math display="block">v = \frac{6 \times 0.4031}{-2 \times 0.4402 + 12 \times 0.4031 + 3} = 0.3477.</math>
[[Image:CIE illuminant F4 and a blackbody of 2938K.svg|thumb|Relative SPD of FL4 and a [[black body]] of equal CCT. Not normalized.]]
Examining the CIE 1960 UCS reveals this point to be closest to 2938 K on the Planckian locus, which has a coordinate of (0.2528, 0.3484). The distance of the test point to the locus is under the limit (5.4×10<sup>−3</sup>), so we can continue the procedure, assured of a meaningful result:
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[[File:CIE CRI TCS under FL4.svg|thumb|upright=2.8|center|The cyan circles indicate the TCS under the ''reference'' illuminant. The short, black, vectors indicate the TCS under the ''test'' illuminant, before and after chromatic adaptation transformation (CAT). (The vectors are short because the white points are close.) The post-CAT end of the vector lies NW, mirroring the chromaticity vector between the reference and test illuminants.
The special CRIs are reflected in the length of the dotted lines linking the chromaticities of the samples under the reference and chromatically adapted test illuminants, respectively. Short distances, as in the case of TCS3, result in a high special CRI (87.9), whereas long distances, as in the case of TCS8, result in a low special CRI (10.4). In simpler terms, TCS3 reproduces better under FL4 than does TCS8 (relative to a [[black body]]).]]
== Typical values ==
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