Noise Equivalent Power (NEP) is a characteristic value of image sensors, optical amplifiers
or other optical assemblies. The NEP value is defined as the value at which a minimum input power photocurrent is generated that is equivalent to the rms value of the noise at a bandwidth of one hertz
(Hz). It is essentially the lowest detectable power. In another definition, the NEP value is taken to be the rms value of the sinusoidal signal incident on a photosensitive detector that would produce an equivalent signal voltage at the detector output.