Per J. P. Gilliver (John):
. Every camera I've played with that claims to have night
vision (and I'm sure does) by using IR LEDs, has ones which make a
perfectly visible red glow; as Pete says, it seems odd that they are.

I've read references to IRs that emit on a different freq that is
not visible to the human eye. In fact, I've got a game camera
that takes still photos whose flash is not visible.

Must be some logical reason why they use the visible freq on most
surveillance cams... but what? Cost? Efficiency?
--
Pete Cresswell