Scintillation is change of light from bright light to dim light in a given period of time

Scintillation is change of light from bright light to dim light in a given period of time. The intensity of light changing is called atmospheric scintillation of a receiver that detects the signal from a transmitter. In other term, scintillation degrades Free Space Optics performance due to its temperature fluctuations of the signals received at the detector that is caused by variation in refractive indicator in transmitting path because of the temperature change. These indicators change because of the atmosphere to act like a series of small lenses that deflect portions of the light beam into and out of the transmit path.
The time scale of these fluctuations is of the order of milliseconds, approximately equal to the time that it takes a volume of air the size of the beam to move across the path, and therefore is related to the wind speed. Scintillation can change by more than an order of magnitude during the course of a day, being the worst, or most scintillated, during midday when the temperature is the highest.