An illumination device comprising a plurality of solid state light sources and a concentrating wave length converter arranged to inject light from said light sources through at least one entrance surface and to extract wave length converted light from at least one exit surface, comprising a structured layer provided on said exit surface, said structured layer having a structure period less than 5 micrometers, thereby enabling out-coupling through the exit surface by a combination of refraction and diffraction. In a situation where the angle of incidence on a surface is within a limited range, a combination of refraction and diffraction may provide a superior out-coupling from that surface.