Dark Current
Charge that accumulates in a photosite from thermal energy rather than from light, growing with exposure time and temperature.
Measured in
e⁻/s
In depth
Dark current roughly doubles for every 6 to 8 °C rise in sensor temperature, which is why long exposures on a warm night are visibly noisier than the same exposures in winter. It is deterministic enough to be measured and subtracted with a dark frame, and it is the reason astronomical cameras are actively cooled.
Examples in practice
A five-minute exposure on a hot evening shows a visible red glow in one corner that the same exposure in frost does not.