The “Dark Offset” or “Dark Voltage” or “Dark Current” or “The Dark” is the baseline reading from the instrument when there is no light. Dark voltages are almost always a function of instrument temperature. Dark voltages are typically small relative to the dynamic range of a sensor, but are significant when measuring low light levels. Dark voltages may be positive or negative. A dark segment is an interval of readings in a data file that indicate the values that may be used as darks when preprocessing or processing the data.