As photons of light (small circles) enter the CCD, they are absorbed by a silicon layer if they have sufficient energy. Each absorbed photon causes an electron to be promoted into the conduction band of the silicon. After the exposure is completed, the CCD then moves the conduction electrons sequentially by applying charge (shown in red.) A detection device (upper left corner in this movie) counts the electrons. Knowing the timing sequence gives the location of the original incident photon.