When Jesse Porter is finished interrogating Kendra the room is rather dark. When he exits, the room can clearly be seen brightly lit, in the next shot it is dark again.
Michael and Fiona find a can of "IR paint" (infra-red). Michael later uses a black light (ultraviolet or UV) to reveal marks made with the IR paint. Infra-red and ultraviolet are completely different (IR has a longer wavelength than visible light; UV has a shorter wavelength).