Pyranometers (from the Greek word for fire) were designed specifically for measuring isolation. Isolation is the solar flux density i.e. was measured in watt/square meter. A digital pyronometer is an instrument which is used to measure the total of the solar radiation at the surface of the earth .Hare we introduce a series of argument on the mechanics of exchanges and thermal balance. Moreover with this instrument, a quantitative study of the solar energy is made possible