Readout Amplifier Glow

All semiconductor devices emit light when power is applied.

The readout amplifier in the corner of a CCD array therefore creates a small amount of light when it is powered up. This causes a bright spot in the corner of the array. This is often minimized by partially powering down the amplifier during integration, and then restoring it to full power during readout.

The A/D converters at the top and/or bottom of every column in a CMOS array also produce light.  Since there are more transistors this can cause a large amount of glow.  Some sensors intended for long exposure operation include means to reduce the generated light during the exposure.