Light decay generally refers to its luminous flux. When charging the surface of the photosensitive drum, as the charge accumulates on the surface of the photosensitive drum, the potential continues to increase, and finally reaches the "saturation" potential, which is the highest potential.

Optical Power Meter is used to measure the absolute optical power or the relative loss of optical power through a section of fiber. In fiber optic systems, measuring optical power is fundamental, much like a multimeter in electronics.