What is Direct radiation?
Solar radiation received in the form of direct solar beams not blocked by clouds or other atmospheric obstacles. It is measured by a pyrheliometer with an acceptance angle of 5.7°. Sunlight and heat from direct irradiance is perceived as sunshine. Sunshine duration is defined by WMO as the total time during which direct radiation equal to or exceeding 120W/m2 is received by a specified area. Also known as direct beam radiation or beam radiation.