Painting it black would certainly help. Carbon black would be good. You could also go further by placing painted rectangular spikes on the walls. We use specially painted spikes made of a foam like material in anechoic chambers to absorb radiation. The structure is pretty good for absorbing just about any kind of wave as it is also used in audio anechoic chambers. While they wouldn't be properly designed for visible light they would induce more backscattering and help break up the reflections that would normally send the light further down the corridor.Yes light bulb and a corridor, that is what I thought. Is there any way to prevent all reflection. Maybe painting the corridor black.