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daylight
Daylight, or the light of day, is the combination of all direct and indirect sunlight during the daytime. This includes direct sunlight, diffuse sky radiation, and (often) both of these reflected from the Earth and terrestrial objects. Sunlight scattered or reflected from objects in outer space (that is, beyond the Earth's atmosphere) is not generally considered daylight. Thus, moonlight is never considered daylight, despite being "indirect sunlight". ''Daytime'' is the period of time each day when daylight occurs. Daylight happens because the earth rotates and either side the sun shines on is considered daylight.
== Definition ==
Daylight is present at a particular location, to some degree, whenever the sun is above the horizon at that location. (This is true for slightly more than 50% of the Earth at any given time. For an explanation of why it is not exactly half, see here). However, the outdoor illuminance can vary from 120,000 lux for direct sunlight at noon, which may cause eye pain, to less than 5 lux for thick storm clouds with the sun at the horizon (even <1 lux for the most extreme case), which may make shadows from distant street lights visible. It may be darker under unusual circumstances such as a solar eclipse or very high levels of atmospheric smoke (See New England's Dark Day), dust,〔http://www.perryton.com/black.htm〕 or volcanic ash.〔http://volcanoes.usgs.gov/ash/〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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