< How did the old light-pens or the light-gun with Atari 8-bits work ? <Weren't they related to this sensitivity of the CRT ? Light pens were fast photo diode that did coincidence detection with a scan line that was bright. The logic in the video board(or chip) would map the "hit" to a scan line address... the rest was programming in the form of what was at that spot and was it a "button". Very simple device save for there were timing delays to be compensated for. Allison