Since D65 represents white light, its co-ordinates are also a white point, corresponding to a correlated color temperature of 6504 K . Rec . 709, used in HDTV systems, truncates the CIE 1931 coordinates to x = 0.3127, y = 0.329.
32.
Together with D . L . MacAdam and G . Wyszecki he used in 1964 the method of principal component analysis to demonstrate that natural daylights are largely composed of three components from which daylights at any correlated color temperature can be defined ( CIE method of calculating D-illuminants ) . ( 4)
33.
To deal with the problem of having to compare light sources of different correlated color temperatures ( CCT ), the CIE settled on using a reference black body with the same color temperature for lamps with a CCT of under 5000 K, or a phase of CIE standard illuminant D ( daylight ) otherwise.
34.
Good quality consumer CFLs use three or four phosphors to achieve a " white " light with a color rendering index ( CRI ) of about 80, where the maximum 100 represents the appearance of colors under daylight or other sources of black-body radiation such as an incandescent light bulb ( depending on the correlated color temperature ).
35.
CRI is calculated from the differences in the chromaticities of eight CIE standard color samples ( CIE 1995 ) when illuminated by a light source and by a reference illuminant of the same correlated color temperature ( CCT ), commonly measured in Kelvins, indicating the light color produced by a radiating black body at a certain temperature; the smaller the average difference in chromaticities, the higher the CRI . A CRI of 100 represents the maximum value.
