I recently installed six optocouplers in a two-channel push-pull circuit. I checked the LEDs with an near-infrared viewer before applying high voltage and noticed there s a lot of light coming out of the clear housings. It seemed like a significant amount, compared to ambient light. Will painting the outside of the devices black, or wrapping them in electrical tape cause problems? (electrical breakdown). The concern is the potential for optical cross-talk while operating at 6kV preventing the “off” arm from completing turning off. I also noticed that there are two small holes in the housing (not near any leads) Do these need to be left uncovered?

Cross-talk can be an issue with these devices. Because they are high voltage, many end-users will encapsulate the optocouplers (and surrounding circuitry) with an epoxy or coating to further insulate the optocouplers. This epoxy is usually opaque, so it eliminates the...