The Face ID is an active infrared scan. Most CCDs (digital camera detectors) are sensitive to near-IR, and the IR filters are not perfect so you can see near-IR emitters with most digital cameras.
What's really fun is to take a cheap camera and replace the IR filter with a visible light filter and then the camera ONLY sees in near-IR.
Ok, but I have an important question.
If this real, why then is the light registering in the voilet end of the spectrum... near UV and not the red end of the spectrum where visible light trails off into IR?
I think this is actually an artist's impression of the phenomenon. Because, even if you were in a very foggy room I don't think you'd be able to get this sort of picture where you can "see the beam".
Anyhow, when I've used digital cameras to look for near-IR it has always registered as white, or maybe slightly blue-ish on the display. Why? I'm not certain, but I suspect that's just how the computer interprets the particular voltage that IR produces in the tiny CCD capacitor elements.
Seems reasonable. That said, I think the program that interprets the data from the CCD for the display plays a role, It registers a signal, but doesn't understand that specific signal and reverts to perhaps an "error" color if you will.
What's really fun is to take a cheap camera and replace the IR filter with a visible light filter and then the camera ONLY sees in near-IR.
If this real, why then is the light registering in the voilet end of the spectrum... near UV and not the red end of the spectrum where visible light trails off into IR?
Anyhow, when I've used digital cameras to look for near-IR it has always registered as white, or maybe slightly blue-ish on the display. Why? I'm not certain, but I suspect that's just how the computer interprets the particular voltage that IR produces in the tiny CCD capacitor elements.