A pattern of light that is highest in the corners and decreases towards the center of the detector. Each time the detector is read out, the readout amplifiers, which are situated near the corners of the detector, are turned on. These amplifiers emit IR radiation that is detected by the pixels in the detector - similar to having a small "light bulb" in each corner.
A typical single readout produces about 20-30 ADUs of amp-glow in the corners of the detector, and 2-3 DN near the center. Since the readout time of the detector is the same each time (it takes 0.203 seconds to read the whole image), the on-time for the amplifiers is always the same for each readout, and thus the light pattern seen by the array is repeatable. So in a given readout, the amount of signal due to amp-glow in each pixel scales directly with the number of readouts since the last reset.
A tool to allow users to generate synthetic darks is available.This tool allows the observer to vary the degree of dark current, amp glow, and shading to better match their data.