Measurements of the flux of downward solar radiation through the atmosphere of Venus and at the planetary surface are reported. These were obtained with the interplanetary spacecraft Venera 8 which landed on the surface of Venus on 22 July 1972 after a 55-min parachute descent through the atmosphere. A significant flux of solar radiation was found to penetrate the entire thickness of the atmosphere, with the amount at the ground ∼1.5% of that incident on the top of the atmosphere. The variation of flux with altitude indicates that the clouds have a lower boundary at an altitude of σ35 km. Abstract Measurements of the flux of downward solar radiation through the atmosphere of Venus and at the planetary surface are reported. These were obtained with the interplanetary spacecraft Venera 8 which landed on the surface of Venus on 22 July 1972 after a 55-min parachute descent through the atmosphere. A significant flux of solar radiation was found to penetrate the entire thickness of the atmosphere, with the amount at the ground ∼1.5% of that incident on the top of the atmosphere. The variation of flux with altitude indicates that the clouds have a lower boundary at an altitude of σ35 km.