Abstract
A series of measurments of the colour temperature of daylight (north skylight, east skylight and south skylight including direct sunlight) have been made at about noon at Nagaoka city in Niigata prefecture with spectrophotometer. The colour temperature of daylight under fine sky conditions is variable between 6, 000 K and 30, 000 K and its mean value is about 10, 200 K. Under cloudy and rainy conditions it varies between 4, 300 K and 9, 500 K and its mean value is about 6, 250 K. The colour temperature of north skylight varies very much and its mean value is about 7, 350 K. Variation of south skylight including direct sunlight is little and its mean value is about 6, 020 K. East skylightis similer to north skylight.
The chromaticity coordinates (x, y) computed from the spectral distributions cluster about
y=3.271x-3.861x2-0.319
In the visible region, spectral distributions of daylight agree very well with those CIE reconstituted daylight but in near-ultraviolet region it is slightly higher than CIE.
