smx wrote:Is there infrared light of some specific frequency that is 1. invisible to human eye and 2. can be picked up much more strongly by the normal Rpi camera than in the picture you've given? Or any other way to have "normal" colors plus infrared illumination?
You can play around with near-IR LEDs around 690 - 770 nm and see if they work well enough, the camera will see them better than your eye, but if you mean "truly invisible" even at night, you don't really get that until you're out around 940 nm. But for normal daytime use, a low-power LED around that wavelength range may be good enough.
Remember, if you have an indoor area which is lit by fluorescent light (no incandescent or sunlight), there is very little IR naturally present. That means even the IR version of the camera will see normal color, because the IR version *is* simply the normal version without the IR-blocking filter, and if there is no IR to begin with, then the camera gets the same wavelengths anyway even without the filter. Then, if you have small IR LEDs they will show up brightly in the camera image, but the colors of other things will remain normal (so long as the IR LEDs aren't so brightly shining on other things they are overwhelming the normal lights. With standard 5mm diameter LEDs and normal light levels, that is likely not a problem).
By the way, I'm using one of the Pi IR cameras right now looking out a window, and the colors look almost normal, maybe just a little unsaturated. On a cloudy morning there isn't that much IR even outdoors. The sky color at the edge is caused by vignetting from a cheap fisheye lens adapter.