S-1 Sunlight Mercury Discharge

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.
Manufacturer: General Electric Co. of U.S.A.
Lamp Power: 400 Watts
Lamp Current: 27.5 Amps 9.5A at starting
Lamp Voltage: 14.5 Volts 30V at starting
Cap: E39s/41 Ni plated brass
Bulb Finish: Inside Frosted borosilicate Transmitting to 280nm
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 to 50% survival
Warm Up / Re-strike Time: 5 minutes to full UV output Instantaneous restrike
Factory: Nela Park, Ohio U.S.A.
Date of Manufacture: Circa 1950
Original Value: US $4.75 (1948)
References: 1) GE Lamp Catalogue, USA, 1948, p.30
2) Weitz, C.E., GE-Mazda Lamps - Characteristics & Applications (Bulletin LD-1) , General Electric U.S.A., 1939