||In 1932 GE's Lighting Headquarters at NELA Park unveiled this most unusual light source to the world, the S-1 Sunlight lamp. It was conceived by Matthew Luckiesh to deliver a light output closely resembling that of the sun. His goal was to develop a light source with the same mild ultraviolet content as natural daylight, in the belief that irradiating people with this light would give them vitality and maintain health. Judging from the spectacular sales of the lamp, the public seemed to believe this marketing as well.
This lamp is a large 400W source which was employed with a separate reflector standing about five feet above the ground, providing its sunlight rays to complement the lighting in any room of the home. Initially the lamp was manufactured with a clear bulb, but owing to the high intrinsic brilliancy of the source and the consequent glare, from 1939 onwards it was only made with this inside frosted pearl bulb. Shortly before this time, in 1937 the smaller S-2 lamp was introduced for treatment of small surfaces.
The lamps consist essentially of a V-shaped tungsten filament with heavy windings around the tails to increase the thermal mass here. It is sealed inside a UV-transmitting hard glass bulb which contains a sizeable pool of liquid mercury and low pressure argon. When illuminated on a low voltage high current transformer, the filament lights and thermionic emission takes place. As the mercury begins to vaporise and the gasfilling becomes conductive at the voltage available, an arc gradually builds up across the ends of the filament. The filament continues to decrease in intensity as the arc short-circuits it, but remains lighted at all times, the ionised mercury vapour contributing the ultraviolet spectral output.