Abstract: The invention relates to an illumination system (2), aluminaire (2), a backlighting system and a display device. The illumination system according to the invention comprises a light exit window (30) for emitting light from the illumination system, and a diffuse reflecting screen (40) arranged opposite the light exit window. The illumination system further comprises a light source (20) which is arranged for indirect illumination of the light exit window via the diffuse reflecting screen. The light source is arranged near an edge of the light exit window on an imaginary plane (22) arranged substantially parallel to the light exit window and emits light away from the light exit window. The illumination system further comprises an edge wall (62) comprising a specular reflecting mirror (60) being concavely shaped for reflecting at least part of the light emitted by the light source towards the diffuse reflecting screen.