The detector shift registers generate light which is in turn detected by the detector. These glows are visible on 4 quadrants of the detector, at the bottom and top of the image. Although strongest in NDR, they can also be seen in DCR. The glow subtracts out perfectly when subtracting sky or dark frames that have been taken with the same DIT. Moreover, most of the glow is outside the useful part of the image in spectroscopy, and the noise induced by the glow is negligible in the useful part.