Sky luminance distribution models have been recommended by the International Commission on Illumination (CIE) for the design of daylighting schemes. Recent developments relate to “all-sky models” for modeling sky luminance under weather conditions ranging from clear to overcast.
The Sun is not the only object that may appear less blue in the atmosphere. Distant clouds or snowy mountaintops may appear yellowish. The effect is not very obvious on clear days but is very pronounced when clouds cover the line of sight, reducing the blue hue from scattered sunlight.