Insolation means the radiation absorbed by the earth and radiation means the radiation emitted by sun is known as radiation
Insolation-insolation(from Latin insolare, to expose to the sun) is the total amount of solar radiation energy received on a given surface area during a given time. It is also called solar irradiation and expressed as "hourly irradiation" if recorded during an hour or "daily irradiation" if recorded during a day.
radiation-The emission and propagation of energy in the form of rays or waves. The energy radiated or transmitted in the form of rays, waves, or particles. A stream of particles or electromagnetic waves that is emitted by the atoms and molecules of a radioactive substance as a result of nuclear decay.