||The Rectalux lamp was invented in 1934 by Jan Bergmans at Philips Eindhoven - better known for his development of the similar Cornalux lamp which still remains in production today. The idea was to improve the efficiency of public lighting installations, which at the time typically consisted of ordinary clear incandescent lamps mounted in simple open reflectors. Whereas the Cornalux lamp is intended for indoor use to throw a broad beam of light for the illumination of ceilings, the Rectalux lamp is a higher wattage device providing a rectangular beam for streetlighting service.
The bulb is of a special shape to deliver the required optical distribution, and the upper surface bears an internal aluminised coating. The clear front window has a textured external surface, which provides a moderate degree of diffusion to achieve a uniform light distribution free of filament images. The filament is mounted in a compact grid-shaped assembly, and is located with high accuracy at the desired position in the bulb. A pair of metal wires welded to the mount assembly serve as focussing guides, and during sealing of the mount into the bulb these are aligned with a pair of ridges moulded into the exterior surface of the glass bulb. A 3-pin bayonet cap provides a positive location in the lampholder, and ensures that when the lamps are replaced the beam distribution is not changed.
Although technically a novel approach, the high price of the Rectalux lamps limited their popularity. Also from the mid 1930s incandescent lamps in Europe were progressively replaced by discharge types in street lighting applications. However the Rectalux remained popular in some markets and continued in production in France until the early 1960s.