Abstract: A panel light emitter such as a backlight for displays, has light sources of different colours, (20, 420), a cavity (30) illuminated by the light sources, to mix the light, the cavity having an output surface (35), to output some of the light and a partially reflective coating or layer (40, 440), to provide enhanced reflection back into the cavity of the light incident on the output surface, more than occurs from a difference of refractive index between the output surface and the cavity. The enhanced reflection is non selective of wavelength or polarization. The partially reflective film or coating can be a reflective material having a pattern of apertures. The enhanced reflection can help provide more mixing in the cavity for a given depth of cavity, or enable the depth to be reduced for example.