Westinghouse 'CX' Mild Ultraviolet Incandescent

The so-called 'CX' incandescent lamps appear to have been introduced in the late 1920s, and were offered by both Westinghouse and GE. They provide a source of mild ultraviolet radiation along with infrared and visible light.

Ordinary incandescent lamps deliver a continuous spectrum, the vast majority of which is radiated in the infrared spectrum. A small quantity is of course also emitted in the visible wavelengths. The filament in fact produces about 1% ultraviolet radiation as well, but much of this is absorbed by the glass bulb. The CX lamps attempted to remedy that shortcoming by making the bulb from a special glass having reduced concentration of the usual iron (III) oxide impurity, which is responsible for the slight greenish hue of ordinary soda-lime silicate glasses and their consequently poor UV transmission. As such this lamp radiates a full spectrum right down to just under 300nm.

The filament runs slightly hotter than a normal incandescent lamp of the same power, so as to further increase the UV flux. It may seem unusual that it is not driven much harder still, but it must be remembered that the highest loaded "photoflood" style incandescent lamps were not introduced until 1932, rather later than the origin of this lamp. Their application also called for a relatively long lifetime.

CX lamps were often used for the treatment of skin conditions, where the small ultraviolet component was beneficial. They were produced in 60W A19, 250W G30 and 500W G40 ratings until the 1940s, but had been generally supserded even in the 1930s by more efficient ultraviolet mercury sunlight lamps like the S-1 and Ultra-Vitalux.
Manufacturer: Westinghouse
Lamp Power: 250 Watts
Lamp Voltage: 120 Volts
Lamp Current: 2.08 Amperes
Cap Type: E26s/25 Brass & Vitrite
Bulb Type: G-95 G-30 in eighths/inch
Bulb Finish: UV-transmitting Inside Frosted
Filament Type: C-7A/3s Single Coil Wreath-Vee
Atmosphere: Argon-Nitrogen Red P getter
Luminous Flux: 4075 Lumens
Luminous Efficacy: 16.3 Lumens per Watt
UV-A Flux: 0.3 Wrad 320-400nm
UV-A Irradiance: 30 mW/m² @ 1 metre
Colour Temperature / CRI: CCT: 2900K Ra: 100
Chromaticity Co-ordinates: CCx: 0.445 CCy: 0.407
Lifetime: Estimated ~500 hours
Burning Position: Universal
Overall Length: 152 mm 6 inches
Light Centre Length: 101 mm 4 inches
Factory: U.S.A.
Date of Manufacture: Approx. 1930
Original Value:
References: 1) Mazda Lamps Characteristics & Applications, C.E.Weitz, Bulletin LD-1, publ. General Electric USA, August 1939 p.35.
2) Industrial Electric Lamps & Lighting, E.S.Lincoln, publ. Essential Books USA, 1945, pp.48-49.
3) The Scientific Basis of Illuminating Engineering, P.Moon, publ. Dover Publications Inc. USA, 1961, p.41
4) Photometric measurement