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SOX Low Pressure Sodium with IR Coating
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Updated
02-XI-2015 |
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The final great breakthrough in improving the thermal insulation of sodium lamps came in 1964, when thin heat-reflecting films of exotic materials were introduced. A microscopically thin coating on the inside of the outer jacket successfully dispensed with the cumbersome heat-reflecting glass sleeves of the SOI design. Film composition and thickness is arranged such that they reflect the infrared while still allowing the visible light to pass through. Initially a 50-nanometre film of pure gold was employed, on the Linear sodium range. This remains the best heat reflector, but it also absorbs a lot of light. Bismuth was tried in some German lamps, but the biggest improvements came with the use of metal oxide semiconductor films and the name SOX was introduced with these lamps. These materials can be doped so that they have high infrared reflectivity, while still being transparent to visible light.
Between 1964 and 1967 a range of SOX lamps having stannic oxide coatings was marketed. Because of the great increase in efficacy, lamp wattages had to be reduced. This material was superseded in 1967-68 with a 0.32 micron coating of tin-doped indium oxide, the film still employed in today's SOX lamps. The corresponding increase in efficacy saw the SOX lamps re-rated once again.
A further improvement was made in 1983 with so-called SOX-E lamps. These employ a film of greater thickness which delivers improved heat reflection. Lamp power had to be reduced again to prevent overheating, with the reduced current density leading to efficacies up to 200 lm/W. Some types feature an advanced platinum catalyst in the outer jacket to crack hydrdocarbon vapours and further reduce conducted heat losses.
Incidentally it is often possible to tell the coating type from the colour of surface reflections in the film. Stannic oxide lamps produce a yellow/orange colour, indium oxide takes on a greenish hue, while SOX-E coatings impart a reddish colour to reflected light. |
| | Tin Oxide Lamps |
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Philips |
40W |
| SO-X with IR coating of stannic oxide |
| 1963 |
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Osram-GEC |
40W |
| SOX/H with IR coating of stannic oxide |
| 1967 |
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| | Indium Oxide Lamps |
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Philips |
90W |
| SO-X of Philips' first indium construction |
| 1968 |
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Philips |
35W |
| SO-X of Philips' first indium construction |
| 1971 |
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Philips |
90W |
| SOX with improved inner support assembly |
| 1988 |
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Philips |
35W |
| SOX-Plus design with increased service life |
| 1996 |
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Philips |
35W |
| SOX-PSG with increased reliability and service life |
| 2003 |
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Osram-GEC |
90W |
| SOX/H 1st generation : Dimpled discharge tube |
| 1967 |
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Osram-GEC |
55W |
| SuperSOX 2nd gen.: Ring Moulds & Graded Film |
| 1978 |
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Osram-GEC |
90W |
| SuperSOX 3rd gen.: Improved top support |
| 1983 |
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Osram |
55W |
| SuperSOX 4th gen.: Improved top support |
| 1993 |
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Osram |
35W |
| SOX-Plus 5th gen.: Improved top support |
| 1996 |
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Osram |
55W |
| SOX 6th gen.: Manufactured by Philips |
| 2003 |
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Thorn |
135W |
| SOX lamp of Thorn's second generation |
| 1983 |
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Thorn EMI |
35W |
| SOX lamp of Thorn's second generation |
| 1986 |
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GE-Thorn |
35W |
| SOX lamp of Thorn's third generation |
| 1991 |
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GE |
35W |
| SOX-Plus with increased life guarantee |
| 2004 |
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| | Improved Indium Oxide (Economy) Lamps |
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Philips |
26W |
| SOX-E Economy with improved efficacy |
| 1984 |
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Osram-GEC |
26W |
| SOX-E Economy with improved efficacy |
| 1985 |
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GE |
26W |
| SOX-E Economy with improved efficacy |
| 2003 |
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Philips |
36W |
| SOX-E PSG with solid-state getter |
| 2012 |
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| | Miniature Lamps |
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Philips |
18W |
| Mini-SOX lamp for security lighting |
| 1977 |
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Osram-GEC |
18W |
| Miniature 18-watt lamp for security lighting |
| 1981 |
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Osram-GEC |
10W |
| Miniature 10-watt lamp for security lighting |
| 1981 |
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Thorn |
6W |
| Experimental 6-watt miniature lamp |
| ~1985 |
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Philips |
18W |
| Experimental 18-watt improved efficacy lamp |
| ~1985 |
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