Solar radiation, also known as sunlight or the solar resource, is the energy emitted by the Sun in the form of electromagnetic waves. It is the primary energy source for most processes in the atmosphere, hydrosphere, and biosphere. Solar radiation can be captured and turned into useful forms of energy, such as electricity, through the use of solar panels.

There are two types of solar radiation:

• Direct beam solar radiation: This is the solar radiation that reaches the Earths surface without being diffused.

• Diffuse solar radiation: This is the solar radiation that has been scattered, absorbed, and reflected by the atmosphere, clouds, dust, and other particles before reaching the Earths surface.

The sum of the direct beam and diffuse solar radiation is called global solar radiation. Atmospheric conditions can reduce direct beam radiation by 10% on clear, dry days and by 100% during thick, cloudy days.

Solar radiation affects plant metabolism and animal behavior. The study and measurement of solar radiation have several important applications, including the prediction of energy generation from solar power plants, the heating and cooling loads of buildings, climate modeling and weather forecasting, passive daytime radiative cooling applications, and space travel.

Solar radiation is measured in watts per square meter (W/m2) in SI units. The amount of solar radiation received on Earth depends on several factors, including the distance from the Sun, the solar cycle, the tilt of the measuring surface, the height of the Sun above the horizon, and atmospheric conditions. Scientists measure the amount of sunlight falling on specific locations at different times of the year and estimate the amount of sunlight falling on regions at the same latitude with similar climates.