By using low-pass optical filters on cameras, for example like this one (probably much cheaper in volume): https://www.edmundoptics.com/document/download/396359

By using low-pass optical filters on cameras, for example like this one (probably much cheaper in volume): https://www.edmundoptics.com/document/download/396359 https://www.edmundoptics.com/document/download/396359 I've used band-pass filters which reject everything except a narrow band, so that camera sees just the IR LED (chosen to fall in the middle of passed band) and they cost a few USD in small volumes.