a few distinguishing features: 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. Adaptation of all colors to D65 (since CIELAB is well-tested under D65). It is conventional to use the original method; R96a should be explicitly mentioned if used. New test color samples As discussed in , recommends the use of a ColorChecker chart owing to the obsolescence of the original samples, of which only metameric matches remain. In addition to the eight ColorChart samples, two skin tone samples are defined (TCS09* and TCS10*). Accordingly, the updated general CRI is averaged over ten samples, not eight as before. Nevertheless, has determined that the patches in give better correlations for any color difference than the ColorChecker chart, whose samples are not equally distributed in a uniform color space. Example The CRI can also be theoretically derived from the spectral power distribution (SPD) of the illuminant and samples, since physical copies of the original color samples are difficult to find. In this method, care should be taken to use a sampling resolution fine enough to capture spikes in the SPD. The SPDs of the standard test colors are tabulated in 5 nm increments , so it is suggested to use interpolation up to the resolution of the illuminant's spectrophotometry. Starting with the SPD, let us verify that the CRI of reference illuminant F4 is 51. The first step is to determine the tristimulus values using the 1931 standard observer. Calculation of the inner product of the SPD with the standard observer's color matching functions (CMFs) yields (X, Y, Z) = (109.2, 100.0, 38.9) (after normalizing for Y = 100). From this follow the xy chromaticity values: The next step is to convert these chromaticities to the CIE 1960 UCS in order to be able to determine the CCT: 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 (5.4×10−3), so we can continue the procedure, assured of a meaningful result: We can verify the CCT by using McCamy's approximation algorithm to estimate the CCT from the xy chromaticities: where . Substituting yields n = 0.4979 and CCTest.