An optical element for obtaining a skylight appearance and a luminaire

An optical element for use in front of a light source for obtaining a skylight appearance, said optical element having an element light input window and an element light exit window;

• wherein the optical element comprises a raster structure situated at the element light input window, a diffuser situated at the element light exit window opposite of the raster structure, and an edge wall extending between the raster structure and the diffuser;
• the raster structure, the diffuser and the edge wall defining a chamber;
• wherein the raster structure comprises a plurality of light transmitting cells, each light transmitting cell comprising:
• a light transmitting channel for collimating a part of light emitted by the light source,
• a light input window at a first side of the light transmitting channel for receiving light from the light source,
• a light exit window for emitting light, at least a part of the light exit window being arranged at a second side of the light transmitting channel opposite to the first side, and
• a wall interposed between said light input window and said part of the light exit window, the wall enclosing the light transmitting channel, at least a part of the wall being transmissive in a predefined spectral range for obtaining a colored light emission at relatively large light emission angles with respect to a normal to the part of said light exit window;
• and, a surface of the edge wall arranged perpendicular to the raster structure being specularly reflective for specularly reflecting the light emitted from the raster structure and impinging on said surface of the edge wall towards said diffuser.