Abstract: A signal lamp whose frustoconical or frustopyramidal housing contains a square or cylindrical light emitting diode and has a rear wall which is completely surrounded by an endless rear edge portion of the sidewall of the housing. The rear wall constitutes or is disposed behind a plate-like carrier for the diode and one or more series resistors, and such rear wall can be bonded directly to the front side of the front wall of a switch box, control panel or the like. The front end of the housing has a square or rectangular aperture for the front wall of the light-transmitting envelope of the diode. The conductors which connect the diode to an energy source pass through one or more hollow projections which extend from the rear wall of the housing and through one or more complementary openings of the front wall.