Sunlight

Sunlight shining upon two different sides of the U.S. state of New Jersey. Sunrise on the Jersey Shore at Spring Lake, Monmouth County (above), and sunset on the Shore at Sunset Beach, Cape May County (below). Both are filtered through high stratus clouds.

Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible light perceptible to the human eye as well as invisible infrared (typically perceived by humans as warmth) and ultraviolet (which can have physiological effects such as sunburn) lights. However, according to the American Meteorological Society, there are "conflicting conventions as to whether all three [...] are referred to as light, or whether that term should only be applied to the visible portion of the spectrum."^[1] Upon reaching the Earth, sunlight is scattered and filtered through the Earth's atmosphere as daylight when the Sun is above the horizon. When direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat (atmospheric). When blocked by clouds or reflected off other objects, sunlight is diffused. Sources estimate a global average of between 164 watts to 340 watts^[2] per square meter over a 24-hour day;^[3] this figure is estimated by NASA to be about a quarter of Earth's average total solar irradiance.

The ultraviolet radiation in sunlight has both positive and negative health effects, as it is both a requisite for vitamin D₃ synthesis and a mutagen.

Sunlight takes about 8.3 minutes to reach Earth from the surface of the Sun.^[4] A photon starting at the center of the Sun and changing direction every time it encounters a charged particle would take between 10,000 and 170,000 years to get to the surface.^[5]

Sunlight is a key factor in photosynthesis, the process used by plants and other autotrophic organisms to convert light energy, normally from the Sun, into chemical energy that can be used to synthesize carbohydrates and fuel the organisms' activities.

Daylighting is the natural lighting of interior spaces by admitting sunlight. Solar irradiance is the rate of solar energy received by a unit area from sunlight.

^ "Sunlight". Glossary of Meteorology. Anerican Meteorological Society. Retrieved 2025-03-23.
^ "Climate and Earth's Energy Budget". earthobservatory.nasa.gov. 14 January 2009. Retrieved 2022-01-27.
^ "Basics of Solar Energy". Archived from the original on 2016-11-28. Retrieved 2016-12-06.
^ Bell Burnell, S. Jocelyn (2004). An Introduction to the Sun and Stars (illustrated ed.). Cambridge University Press. p. 56. ISBN 9780521546225. Extract of page 56
^ "The 8-minute travel time to Earth by sunlight hides a thousand-year journey that actually began in the core". SunEarthDay.NASA.gov. NASA. Archived from the original on 2012-01-22. Retrieved 2012-02-12.

[1] "Sunlight". Glossary of Meteorology. Anerican Meteorological Society. Retrieved 2025-03-23.

[2] "Climate and Earth's Energy Budget". earthobservatory.nasa.gov. 14 January 2009. Retrieved 2022-01-27.

[3] "Basics of Solar Energy". Archived from the original on 2016-11-28. Retrieved 2016-12-06.

[4] Bell Burnell, S. Jocelyn (2004). An Introduction to the Sun and Stars (illustrated ed.). Cambridge University Press. p. 56. ISBN 9780521546225. Extract of page 56

[5] "The 8-minute travel time to Earth by sunlight hides a thousand-year journey that actually began in the core". SunEarthDay.NASA.gov. NASA. Archived from the original on 2012-01-22. Retrieved 2012-02-12.

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