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S-1 Sunlight Mercury Discharge |
It is a most unusual kind of hybrid incandescent-discharge source. The bulb is is of a special UV-transmitting hard glass, and is filled with an enormous quantity of liquid 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 without burning out. When illuminated on a low voltage transformer, the filament lights and thermionic emission takes place. As the mercury begins to vaporise and the gasfilling becomes more conductive, a glow discharge is formed, which gradually transforms into an arc across the ends of the filament, ballasted by the external transformer. The filament continues to decrease in intensity as the arc draws more current, but remains lighted at all times. The filament produces a warm white light plus infrared radiation, while the mercury arc contributes ultraviolet rays.
These lamps were normally employed with a separate wide-beam reflector to complement the lighting in any room of the home, and were also used in offices and hospitals. In 1937 the S-1 was joined by the smaller S-2. Both were initially produced with clear glass, but owing to the high brightness of the arc, from 1939 onwards they changed to the inside frosted pearl bulb illustrated here.
| Manufacturer: | General Electric Co. of U.S.A. | |
| Lamp Power: | 400 Watts | |
| Lamp Current: | 30 Amps | 9.5A at starting |
| Lamp Voltage: | 14 Volts | Approx. 30V at starting |
| Cap: | E39s/41 | Ni plated brass |
| Bulb Finish: | Inside Frosted | #776 borosilicate glass |
| Bulb Type: | PS-70 | PS-22 (in eighths/inch) |
| Overall Length: | 163.5 mm | 6 7/16 inches |
| Light Centre Length: | 127.0 mm | 5 inches |
| Electrodes: | C-2V | Overwound plugged tails |
| Atmosphere: | Argon | 0.9 atm. during operation |
| Luminous Flux: | 7,200 lm | @ 100 hrs |
| Luminous Efficacy: | 18.0 lm/W | @ 100 hrs |
| Colour Temperature & CRI: | CCT: | CRI: |
| Total Ultraviolet Output: | 68,000 E-Vitons | |
| Burning Position: | Vertical base up to horizontal | |
| Rated Life: | 400 hours | 50% survival, ~100% UV flux |
| Warm Up / Re-strike Time: | 5 minutes to full output | Instantaneous restrike |
| Factory: | Nela Park, Ohio | U.S.A. |
| Date of Manufacture: | Circa 1950 | |
| Original Value: | US $4.75 (1948) | |