Definitions for "Direct Radiation"
radiation received on a plane surface i from a small solid angle centered on the sun's disk (a.k.a. beam radiation) [W/m2],   direkte Strahlung
Solar radiation that comes straight from the sun, casting shadows on a clear day.
Light that has traveled in a straight path from the sun (also referred to as beam radiation). An object in the path of direct radiation casts a shadow on a clear day.