| irradiance produced by direct sunlight on a surface on the Earth that is perpendicular to the direction of irradiation by the Sun Note 1 to entry: Normal solar irradiance is not the same as direct solar irradiance, which is measured on a horizontal surface on the Earth, not necessarily perpendicular to the direction of irradiation by the Sun. Note 2 to entry: The normal solar irradiance is expressed in watt per square metre (W·m−2).
|