solar radiation; insolation
Technical term for sunlight energy reaching the earth; used in meteorology, engineering, and environmental contexts.
今日の日射量は平年より多い。
Today's solar radiation is higher than average.
Power generation systems using solar radiation are attracting attention.
日射 is a technical/scientific term for solar radiation or insolation, while 日光 is the common word for sunlight in daily speech.
Compound of 日 (sun) and 射 (shoot, radiate), literally 'sun rays'.