The invention provides a lighting unit comprising a light source and a transmissive optical plate, wherein the light source comprises a light exit surface for light source light, wherein the transmissive optical plate comprises an upstream face directed to the light exit surface of the light source and a downstream face arranged away from the light exit surface) of the light source, wherein the optical plate comprises a 2D array of micro optical elements for refraction of the light source light in a direction away of the downstream face, wherein the geometrical path length from the light exit surface to the transmissive optical plate is at least 20 cm.