[참고] Variations in Natural Light.

Variations in Natural Light.
Radiation from the sun that does get through the atmosphere and is visible to our eyes can be described in three ways:

• Sunlight is light coming directly from the sun — the image of the sun's disk or a shaft of sunlight into a darkened room. The solar color changes significantly across the day and depends on the angle of the sun above the horizon, the altitude of the viewer above sea level, the season, the geographical location and the amount of water vapor, dust and smoke in the air. The sun itself is so brilliant that it overwhelms color vision, making color judgments unreliable, but if the noon sun were dimmed sufficiently, its color would appear a pale greenish yellow (not the deep yellow of schoolroom paintings). This color appears in the positive afterimage of sunlight reflected off a car windshield.

• Skylight refers to the blue light of the sky as viewed from a location in complete shade, for example the light entering through a north facing window. It results from the scattering of short wavelength light by air molecules. This scattering is slightly stronger from the northern sky, opposite the generally southern origin of sunlight. The illuminance contribution of skylight is significant: though much dimmer than the sun's disk, the visible area of the sky is approximately 100,000 times larger, which is why daylight shadows are clearly illuminated and we can read a summer novel in deep shade.

• Daylight is the combined light of sun and sky, for example as reflected from an unshaded sheet of white paper illuminated outdoors. Significant color shifts occur in daylight, depending on geography, season and time of day, but it is unchanged by scattered clouds or overcast: these only dim the light and diffuse it.