Päikese otsese kiirguse vootihedus planeedil või kosmoseaparaadil
the total radiant flux (electromagnetic radiation at all wavelengths) received on a unit area of a given surface; usually measured in watts per meter-squared (W/m2)
Solar irradiance is often integrated over a given time period in order to report the radiant energy emitted into the surrounding environment (joule per square metre, J/m2) during that time period. This integrated solar irradiance is called solar irradiation, solar exposure, solar insolation, or insolation.
The total solar insolation of 1360 W/m2 is the mean solar irradiance per unit area at the mean position of Earth and is measured for a surface that is perpendicular to the solar beam.
Generally insolation is expressed two ways. One unit is kilowatt-hours per square meter (kWh/m2) per day which represents the average amount of energy hitting an area each day. Another form is watts per square meter (W/m2) which represents the average amount of power hitting an area over an entire year.
