 |
In 1929 GE introduced the first succesful ultraviolet lamp, the S-1 Sunlight. It had been conceived by Royal Strickland and Matthew Luckiesh to deliver a spectrum having a mild ultraviolet content resembling that of the sun. It was believed that irradiating people with this light would give them vitality and maintain health.
The S-1 was a large 400W source for general irradiation in public areas, and a smaller domestic source was soon in demand for residential use. Thus in 1937, this 130W S-2 variant was launched. Initially it had a clear glass bulb, but owing to its uses at short ranges its high brightness produced too much glare. From 1939 onwards both this and the larger S-1 were only made with inside frosted pearl bulb.
It is a most unusual kind of hybrid incandescent-discharge lamp. The bulb is is of a special UV-transmitting hard glass, and is filled with an enormous quantity of mercury plus low pressure argon. It contains a V-shaped tungsten filament, whose ends have extra windings to increase their thermal mass such that they can function as electrodes. When illuminated on a low voltage transformer, the filament lights and thermionic emission takes place. As the mercury begins to vaporise a glow discharge is formed, which gradually transforms into an arc across the ends of the filament, ballasted by the transformer. The filament continues to decrease in intensity as the arc draws more current, but remains lighted at all times. It produces a warm white light plus infrared radiation, while the mercury arc contributes ultraviolet rays. The lower power of this S-2 lamp required the addition of the metal cap, to raise the temperature of the mercury pool and increase the UV output. |