High Quality Content by WIKIPEDIA articles! Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light. If the radiation is totally reflected, the radiation pressure is doubled. For example, the radiation of the Sun at the Earth has a power flux density of 1,370 W/m2, so the radiation pressure is 4.6 µPa (absorbed) (see also Climate model). The fact that electromagnetic radiation exerts a pressure upon any surface exposed to it was deduced theoretically by James Clerk Maxwell in 1871 and Adolfo Bartoli in 1876, and proven experimentally by Lebedev in 1900 and by Ernest Fox Nichols and Gordon Ferrie Hull in 1901.