A light source for emitting collimated light in particular for an edge-lit large area luminaire , the light source comprising: a light guide unit having a main front face , a main back face , and at least one lateral coupling face connecting the main front face and the main back face in a thickness direction (d T ), wherein the light guide unit is configured for guiding light received at the at least one lateral coupling face by total internal reflection between the main front face and the main back face , and the main front face comprises a plurality of localized light source regions that are areas with a limited extent in two-dimensions for having light pass there through, wherein the light source regions are surrounded by a non-source region , and a plurality of light emitting units for emitting light into the light guide unit through the at least one coupling face , wherein at least one light emitting unit is configured as a light input coupling assembly to receive collected natural light from a fiber and to provide the received natural light to the light guide unit ; and a collimation unit extending along the main front face and comprising a plurality of collimating elements, wherein each collimating element comprises an input side and an output side, is optically associated to one of the plurality of light source regions , is configured to receive light emerging from the associated light source region at its input side, and to emit collimated light from a respective collimated light emitting region formed at its output side. a light guide unit having a main front face , a main back face , and at least one lateral coupling face connecting the main front face and the main back face in a thickness direction (d T ), wherein the light guide unit is configured for guiding light received at the at least one lateral coupling face by total internal reflection between the main front face and the main back face , and the main front face comprises a plurality of localized light source regions that are areas with a limited extent in two-dimensions for having light pass there through, wherein the light source regions are surrounded by a non-source region , and the light guide unit is configured for guiding light received at the at least one lateral coupling face by total internal reflection between the main front face and the main back face , and the main front face comprises a plurality of localized light source regions that are areas with a limited extent in two-dimensions for having light pass there through, wherein the light source regions are surrounded by a non-source region , and a plurality of light emitting units for emitting light into the light guide unit through the at least one coupling face , wherein at least one light emitting unit is configured as a light input coupling assembly to receive collected natural light from a fiber and to provide the received natural light to the light guide unit ; and a collimation unit extending along the main front face and comprising a plurality of collimating elements, wherein each collimating element comprises an input side and an output side, is optically associated to one of the plurality of light source regions , is configured to receive light emerging from the associated light source region at its input side, and to emit collimated light from a respective collimated light emitting region formed at its output side. <EOS>