PHILIPS Typ 57002B/01 SO 45W Sodium Lamp with Detachable Jacket
Lampe à vapeur de sodium basse pression
Niederdruck Natriumdampflampe
This lamp consists of a tube containing a rare gas under low pressure (for ignition) and a quantity of metallic sodium sealed into each end of the tube. Once the lamp has ignited, it must warm up to the point where the pressure of the sodium vapour is high enough to allow the emission of light from the sodium to predominate over that of the rare gas, which consists of neon with a small amound of argon. The pressure necessary for efficient working of the lamp is about 4 x 10-3 mm Hg which corresponds to a temperature of roughly 280°C.
Thermal losses due to conduction and convection have to be limited as much as possible, and to render them independent from the atmospheric conditions, the discharge tube is enclosed in a dewar vacuum jacket.
This double-walled jacket is provided with a porcelain ring, into which the lamp is fixed by means of its cap and a spring plunger. The end of the ignition strip, which serves as auxiliary electrode, terminates in a fork which fits in a constriction in the vacuum jacket and thus also provides a support for the lamp. Since the vacuum jacket is detachable, it can be used again and again when it becomes necessary to replace the lamp.
At the particular temperature at which thse lamps have to work, sodium vapour is extremely active chemically and quickly attacks all ordinary kinds of glass by reason of its great affinity to oxygen. Normal glass-forming oxides such as SiO2 would be reduced to metallic Si, producing a brown or black discoloration, but if B2O3 is employed as the glazing agent, it is possible to manufacture a type of glass which can withstand the effect of sodium vapour. But a borate glass of this kind has the disadvantage that it is readily soluble in water and, in view of weathering effects, is therefore unsuitable. So, in order to utilise the good sodium-resisting properties of borate glass, it is blown as a thin layer on the inside of an ordinary line-glass tube to produce so-called lime-borate glass.
Due to the poor adhesion of liquid sodium to the glass surface, the metal forms large thin films. If lamps were not burned absolutely horizontally, the sodium would also flow from one end of the lamp to the other, forming large light-blocking mirrors, which offset the gain in efficacy from the reduced staining. To prevent movement of sodium, the glass tube is rilled-in at several points leading to the so-called Bamboo construction. This overcame the sodium film problems and improved lumen maintenance.
Lamp current: 0.6 A
Starting current: 0.54 A
Arc voltage: 65-90 V
Max. striking voltage: 340 V
Luminous flux: 2,700 lm
Luminous efficacy: 41 lm/W
Rated lifetime: 6,000 hours
Warm-up time: 11 minutes
Re-strike time: instantaneous
Date of manufacture: 1950s
Hauteur • Height • Höhe : 237 mm • 9" 3/8
Diamètre • Diameter • Durchmesser : 50 mm • 2"
Mazda SI 45W Sodium Vapour Lamp
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