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Solar irradiance
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<p>Solar irradiance is the <a href="/facts/Power_(physics)/mkaEyRnn">power</a> per unit area (<a href="/facts/Surface_power_density/qQ0tUW9a">surface power density</a>) received from the <a href="/facts/Sun/CadPCVHh">Sun</a> in the form of <a href="/facts/Electromagnetic_radiation/Ynx7ujCW">electromagnetic radiation</a> in the <a href="/facts/Wavelength/kcJU0ymz">wavelength</a>. Solar <a href="/facts/Irradiance/fgHwu7uh">irradiance</a> is measured in <a href="/facts/Watt/VK8oqRrm">watts</a> per <a href="/facts/Square_metre/u5nT9y0W">square metre</a> (W/m2) in <a href="/facts/SI_unit/S7YLglNz">SI units</a>. </p><p>Solar irradiance is often <a href="/facts/Integral/4PeM0mJc">integrated</a> over a given time period in order to report the <a href="/facts/Radiant_energy/8QHpm6KY">radiant energy</a> (<a href="/facts/Joule/9ndq9jD2">joule</a> per square metre, J/m2) during that time period. This integrated solar irradiance is called solar irradiation, solar radiation, solar exposure, solar insolation, or insolation. </p><p>Irradiance may be measured in <a href="/facts/Outer_space/R3LRKyFs">space</a> or at the <a href="/facts/Earth%2527s_surface/HLLmDfj0">Earth's surface</a> after <a href="/facts/Atmospheric/oUpLaGRF">atmospheric</a> absorption and <a href="/facts/Scattering/nMou7lEH">scattering</a>. Irradiance varies in space is a <a href="/facts/Function_(mathematics)/CdReEKCh">function</a> of distance from the Sun, the <a href="/facts/Solar_cycle/QrP4Egea">solar cycle</a>, and cross-cycle changes. Irradiance at the Earth's surface additionally depends on the tilt of the measuring surface, the height of the Sun above the horizon, and atmospheric and cloud conditions. </p><p>The study and measurement of solar irradiance have several important applications, including the prediction of energy generation from <a href="/facts/Solar_power_plant/NpgmEbU2">solar power plants</a>, the heating and cooling loads of buildings, climate modeling and weather forecasting, <a href="/facts/Passive_daytime_radiative_cooling/ljL5fKxN">passive daytime radiative cooling</a> applications, and space travel. Solar irradiance also affects <a href="/facts/Plant_metabolism/zAh2o1Ao">plant metabolism</a> and animal behavior. </p>