An illuminating or light emitting device for use as a headlamp, a signaling lamp or other lamp for shining light in a beam or otherwise. It comprises as its main parts a generally flat transparent illuminating element with a circumferential edge in which a plurality of light emitting elements such as LED's are set. The edges are provided with an inwardly reflecting layer. The front side of the illuminating element is in the form of a light radiating surface, while the rear side is completely covered with an inwardly reflecting layer. Such an illuminating device may have a very flat overall shape, has a low current requirement and has a large homogeneous radiating area. It more especially lends itself to use on vehicles.