An optical element for use in front of a light source for obtaining a skylight appearance, and a luminaire are provided. The optical element comprising a plurality of light transmitting cells in a raster structure, a diffuser and an edge wall. A light source emits light towards the raster structure. The raster structure collimates a part of the light and transmits a further part of the light in a predetermined spectral range. White light and colored light that is transmitted by the raster structure may impinge upon the side wall of the optical element. One face of the side wall is a region of specular reflectivity and will reflect the light that impinges upon it back into the chamber that is formed by the cooperation of the raster structure, the diffuser and the edge wall. Light exits the optical element through the diffuser.