Dark current is a thermally generated charge passing through a photodiode that is not exposed to any light (a signal is generated even when the sensor is completely in the dark). One of the disadvantages of CCD sensors is that the generation of electrons in the pixels is not only dependent on the incident light, but also on the ambient temperature, pixel size, sensor architecture and manufacturing technology. The dark current is caused by the fluctuation of electrons in the sensor material, its value increases with increasing temperature. By lowering the ambient temperature, the dark current can be reduced or eliminated.