S-4 Sunlight Mercury Discharge

In 1929 the 400W S-1 mercury-tungsten Sunlight lamp was placed on the market by GE, and in 1937 was accompanied by its smaller S-2 130W counterpart. Those were based on a low pressure mercury discharge burning across the ends of a tungsten filament in a bulb filled with a large pool of mercury. The UV output was mild and the combined radiation from the filament made them excellent radiators of infra-red, visible and ultraviolet light. Their similarity to the solar spectrum made them highly suitable as general health-giving lamps, with a mild sun-tanning effect.

The market quickly evolved and fuelled a desire for lamps having increased sun-tanning power, with less interest in the full spectrum for general health and well-being. The introduction of the low wattage H-4 quartz mercury lamps proved to be an ideal source of UV, however their outer envelopes blocked the shorter wavelengths required for skin tanning. The H-4 arc tube was therefore sealed into the bulb of the S-2 lamp, having a low iron (III) oxide content glass to enable it to transmit the UV rays, and in 1939 the S-4 lamp was born. It could be operated on a simple inductive ballast and the bulky transformers required for the earlier S-2 lamps could be dispensed with. The S-4 soon became the most popular ultraviolet lamp for suntanning.

The seals in this lamp are especially primitive and pre-date the modern moldybenum foil seals. Each of the tungsten lead wires to the electrodes is glazed in a high expansion glass, and via two other intermediate glasses, is sealed to the quartz tube. The ends of thea rc tube are located in small metal cups which act as heat reflectors, to raise the mercury vapour pressure and increase UV power.
Manufacturer: General Electric Co. of U.S.A.
Lamp Power: 100 Watts
Lamp Current: 0.9 Amps  (1.3 Amps during starting)
Lamp Voltage: 130 Volts  (190 Volts during starting)
Cap: E29s/28 (Admedium Brass)
Bulb Finish: Clear hard glass (transmitting down to 280nm)
Bulb Type: A-60 (A-19 in American units)
Overall Length: 5 5/8 inches  (142.9 mm)
Light Centre Length: 3 7/16 inches (87.3 mm)
Electrodes: Backwound tungsten with thoriated shank
Atmosphere: Inner : Argon  Outer : Nitrogen
Luminous Flux: 3,500 lm
Luminous Efficacy: 35 lm/W
Total Ultraviolet Output: 68,000 E-Vitons
Run-up time: 3 minutes (with 3 minute restrike delay)
Rated Life: 1,000 hours
Factory: Hoboken, N.J., U.S.A.
Date of Manufacture: August 1940
Original / Present Value: Not Known
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