Average daylight

The CIELAB system (1976) strictly standardizes the light source and the observer. CIE recommends three standard sources, A is an incandescent lamp, and B and C are lamps provided with different two-cell Davis-Gibson liquid hlters that simulate noon daylight and average daylight, respectively. Since the main object of the system is to obtain colorimetric results for normal tri-chromats (people with normal color vision), the standard observer must represent the human population with normal... 

Figure 1. The brilliant orange-red emission of Eu (A), contrasted to the bluish-white spectral power distribution of average daylight (B)...

Illuminant C (CIE) n. An approximation of average daylight, bluish, with a correlated color temperature of 671 AY.. It is defined in the wavelength range of 380-770 nm. 

Fig. 11. Spectral distribution of CIE illuminants (26). (1) Standard illuminant Dgj Average daylight (including ultraviolet wavelength region) with a correlated color temperature of 6S04K should be used for measuring specimens which will be illuminated by daylight...

The daylight spectrum at the earth s surface is extremely variable because of the effects of aerosols and clouds (i.e. weather) and is also found to vary at different places and at different seasons. Measurements of the daylight spectrum on the earth have been used repeatedly to provide standardized values for specific conditions. The average daylight means the relative spectrum of the total radiation received during a whole day, month or year. 

The MacAdam ellipses, plotted on the w, v diagram, are more uniform in size and orientation than in the CIE diagram. Without recourse to nonlinear transformations, this is about the greatest degree of uniformity possible. These data and the CIE s color difference equations are recommended for use under conditions in which the observer is assumed to be adapted to average daylight they are not recommended by the CIE for other conditions of adaptation. 

K and appears to be bluish white. The CIE Standard Illuminant D65 (Figure 12.2b) is a commonly used standard illuminant that tries to portray standard illumination conditions in the open air in different parts of the world. It represents average daylight and has a CCT of approximately 6500 K (exactly 6504 K). The CIE 1931 color space chromaticity coordinates of D65 are x = 0.3128,3 = 0.3290, which is close to a white-point in the CIE diagram. 

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