This energy travels about 150 million kilometers (93 million miles) through space to reach the top of Earth's atmosphere. Solar radiation, often called the solar resource or just sunlight, is a general term for the electromagnetic radiation emitted by the sun. Waves of solar energy radiate, or spread out, from the Sun and travel at the speed of light through. Solar irradiance is the solar energy flux density outside Earth's atmosphere at a distance from the Sun of 1 Astronomical Unit (AU), given in SI units of Watts per square meter (W/m 2). The sun's total energy input reaching Earth is called total solar irradiance, or TSI. 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. Solar radiation reaches the Earth approximately 93 million miles, which is about 150 million kilometers from the Sun.
