or one of the side walls 44 46 an array 82 of light emitting diodes 84 is mounted by a printed circuit board 86 in a conventional fashion the diodes 84 being arrayed in a linear pattern essentially centered on the board 86 and centered within the sign 40 in that plane in which the board 86 lies it is preferred that the plane of the board 86 be perpendicular to the respective planes within which the back wall 52 and the front wall panel 56 lie so that the diodes 84 are held in a favorable position for illumination of the sign 40 the diode bearing board 86 is mounted at a location spaced from internal surfaces of the bottom wall 50 the plane of the board 86 being immediately below the lowermost extents of the legends 54 72 respectively it is important that the board 86 can be positioned immediately below the lowermost portions of the legends 54 72 in order to provide not only a desired illumination level and evenness of illumination but also a compact sign unit the light emitting diodes 84 are preferably arranged in regularly spaced relation to each other and for the exit sign 40 shown the light emitting diodes 84 are seen to comprise non diffuse narrow viewing angle diodes such as 34 red 34 diodes manufactured.