Dark current is the constant response exhibited by a receptor of radiation during periods when it is not actively being exposed to light.
In physics and electronic engineering, dark current is the relatively small electric current that flows through a photosensitive device such as a photomultiplier tube, photodiode, or charge-coupled device even when no photons are entering the device.
In analytical chemistry, dark current refers to constant response produced by a spectrochemical receptor, even in the absence of radiation. This response adds to the signal produced when the receptor is used to measure light and so must be dealt with to determine how much of the detector response is actually due to the radiation. To compensate for this extra signal, the dark current may be measured in the absence of radiation and then subtracted from the final signal or it is reduced to zero by a compensating circuit. Dealing with dark current is a form of blank correction.