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SO/H Detatchable Low Pressure Sodium
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Updated
04-VI-2015 |
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Developed by Philips in early 1932, the SO/H design was the first commercial sodium vapour lamp to become popular and enter mass production. The discharge tube is U-shaped and fabricated from 2-ply sodium-resistant glass, and to allow this to attain the necessary wall temperature of 260°C for maximum efficacy, it is operated inside a dewar vacuum jacket to provide thermal insulation. At end of life it was customary to replace only the inner tube, the same dewar being used up to about six times, before its vacuum would tend to go soft and no longer provide the necessary insulation.
Although the SO/H lamp was technically superseded by the superior SOI/H 'Integral' design after 1955, it remained in production until about 1965 for replacement purposes. Illustrated here is a selection of SO/H lamps from a variety of manufacturers, exhibiting some of the different construction techniques employed.
It is worth noting here that the rate at which the glasses used in some of these lamps cleans up argon gas can be rather high. In particular, if the lamp has not been lit for more than twenty years or so, the argon gas needed for starting may be adsorped quite rapidly after ignition. If the lamp is then turned off, the loss of this gas makes re-igniton extremely difficult. However if it is left burning for some five hours or so after its first start, this will be sufficient to re-release much of the argon and it will then be safe to turn off the lamp and know that it should strike again. |
| | Philips Lamps |
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Philora |
60W |
| SO/H lamp of Dutch 2nd generation |
| 1938 |
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Philips |
45W |
| SO/H lamp of British design |
| 1952 |
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Philips |
140W |
| SO/H lamp of British design |
| 1951 |
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Philips |
60W |
| SO/H replacement inner of British design |
| 1954 |
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Philips |
45W |
| SO/H replacement Bamboo discharge tube |
| 1957 |
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Philips |
60W |
| SO/H lamp with Bamboo discharge tube |
| 1958 |
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Philips |
85W |
| SO/H lamp with Bamboo discharge tube |
| 1955 |
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Philips |
140W |
| SO/H lamp with Dimpled discharge tube |
| 1958 |
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| | Osram-GEC Lamps |
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OsramGEC |
140W |
| SO/H lamp of early production style |
| 1949 |
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OsramGEC |
45W |
| SO/H discharge tube of last production style |
| 1965 |
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| | BTH-Mazda and AEI-Mazda Lamps |
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Mazda |
60W |
| SO/H lamp with hard glass discharge tube |
| 1950 |
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Mazda |
140W |
| SO/H lamp with hard glass discharge tube |
| 1953 |
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Mazda |
85W |
| SO/H discharge tube of hard glass design |
| 1955 |
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Mazda |
60W |
| SO/H discharge tube of soft glass design |
| 1965 |
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| | Soviet Lamps |
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MELZ |
140W |
| DNAO-140 Soviet Style low pressure sodium |
| 1966 |
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