UV robo-print at Lexel’s pad in NYC

This black frame on the wall appears to frame a empty white page. But when the hidden camera sees a face, it silently snaps a candid photo, and then a bar of UV lights slides down the page, activating the phosphors in the white paper. The UV light energizes the phosphors, lifting an electron into an outer shell, which will eventually decay to release a red photon. So the image slowly fades away, and then the frame looks for the next face.