The invention relates to a light treatment system (10, 12). The light treatment system comprises a light source (20, 22) for emitting light (100) for illuminating a part of a human or animal body (30) for light treatment. The light treatment system further comprises a housing (40, 42) for emitting light towards the part of the human or animal body, and for at least partially covering the illuminated part of the human or animal body from view. The housing further comprises a window (50, 52, 54, 56) for emitting light from an inner part of the housing away from the housing. An effect of the light treatment system according to the invention is that the window in the housing may be used as indicator whether the light treatment system is operating and/or functioning well. Furthermore, the presence of a luminescent material, for example, on the window, may be used as indicator for, for example, ultraviolet light as part of the ultraviolet light may be converted by the luminescent material into visible light.