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RLOD#13 (2020.05.19) Mid-1980s Philips SDW-A 20W The development of the white high-pressure sodium lamp in the late 1970s and early 1980s led to an efficient and durable source of warm-white light with a color not dissimilar from that of incandescent lamps. Philips was a key developer of the technology and they targeted many different applications with this new discharge lamp. One of those applications is automotive headlighting, resulting in the SDW-A 20W shown here. This lamp was designed with the skirted P43t base of the standard H4 halogen lamp so standard car headlights could be retrofitted with the sodium lamp for testing purposes. The tungsten-halogen burner is replaced by a gas-filled glass bulb containing a tiny 20 W high-pressure sodium arc tube provided with finned metal shields. Those elements serve a dual purpose, they limit the size of the luminous source and they control the cold-spot temperature of the burner. The former ensures a good optical compatibility with luminaires designed for incandescent sources, while the later guarantees an optimum burner operation. This concept never made it to the market as the 35 W VeDiLis xenon metal halide lamp system was preferred for the intended application. There are a variety of reasons for that choice, one of which concerned the light color, which for the sodium lamp was deemed too close to that of incandescent lamps. German car manufacturers preferred the cooler white light of metal halide sources as this provides a clear and visible distinction with older headlights, thus setting the new technology apart from a customer point of view. Keywords: Lamps

RLOD#13 (2020.05.19) Mid-1980s Philips SDW-A 20W


The development of the white high-pressure sodium lamp in the late 1970s and early 1980s led to an efficient and durable source of warm-white light with a color not dissimilar from that of incandescent lamps. Philips was a key developer of the technology and they targeted many different applications with this new discharge lamp. One of those applications is automotive headlighting, resulting in the SDW-A 20W shown here. This lamp was designed with the skirted P43t base of the standard H4 halogen lamp so standard car headlights could be retrofitted with the sodium lamp for testing purposes. The tungsten-halogen burner is replaced by a gas-filled glass bulb containing a tiny 20 W high-pressure sodium arc tube provided with finned metal shields. Those elements serve a dual purpose, they limit the size of the luminous source and they control the cold-spot temperature of the burner. The former ensures a good optical compatibility with luminaires designed for incandescent sources, while the later guarantees an optimum burner operation.

This concept never made it to the market as the 35 W VeDiLis xenon metal halide lamp system was preferred for the intended application. There are a variety of reasons for that choice, one of which concerned the light color, which for the sodium lamp was deemed too close to that of incandescent lamps. German car manufacturers preferred the cooler white light of metal halide sources as this provides a clear and visible distinction with older headlights, thus setting the new technology apart from a customer point of view.
2020-05-21_Philips_C011-01.jpg 2020-05-20_Philips_GL92.jpg 2020-05-19_Philips_SDW-A_20W.jpg 2020-05-16_Philips_MHW_70W_D143.jpg RLOD-11_2020-05-15_GE_MVR25021C21U.jpg
Lamp/Fixture Information
Manufacturer:Philips
Model Reference:SDW-A 20W
Lamp
Lamp Type:White sodium
Filament/Radiator Type:Thermal discharge in xenon, mercury and sodium vapors
Base:P43t
Shape/Finish:Tubular clear
Burning Position:Horizontal
Electrical
Wattage:20 W
Physical/Production
Factory Location:Eindhoven, the Netherlands
Fabrication Date:Mid 1980s
Application/Use:Testing and characterization (intention: automotive headlighting)
File information
Filename:2020-05-19_Philips_SDW-A_20W.jpg
Album name:Max / Random lamp of the day
Keywords:Lamps
Filesize:366 KiB
Date added:21 Jul 2025
Dimensions:800 x 1200 pixels
Displayed:40 times
URL:https://trad-lighting.net/gallery/displayimage.php?pid=929
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Comment 1 to 9 of 9
Page: 1

Tuopeek   [Mon 21 Jul 2025 at 21:46]
That’s an awesome lamp and tiny arc tube! Had no idea such a small HPS lamp had been considered. Seem to remember a seeing GEC demonstration of a small HPS lamp for use at home at about the time the Philips compact fluorescent was being launched. Needless to say, with the slow run up and restart times it never appeared. The so-called automotive xenon quickly became popular in vehicle lighting and even a small 10W version I believe appeared for bicycle lights. I wonder if this had become commercial if it would have suffered from an issue I find annoying today. That is the light colour temperature on vehicles and street lighting is much the same making stationary and moving a little harder to differentiate in quickly.
Ria   [Tue 22 Jul 2025 at 14:37]
Amazing as always, Max..! Never seen such a tiny little HPS lamp HPS bulb HD
Max   [Tue 22 Jul 2025 at 16:13]
Thanks Ria. Miniature HID lamps are quite an interesting breed indeed. I have three variants of that 20 W SDW, and a 5 W CDM as well, which has an even smaller burner.

Tuopeek - Good point about the color of LED streetlights vs that of vehicles' headlights nowadays. Maybe that's one reason why car manufacturers pushed for even higher CCTs with the newer LED headlights... To comment on your earlier remark about the potential impact of that issue on the marketability of the xenon metal halide headlight technology back then (early 1990s), personally I don't think streetlight color had any impact at all, it was just a matter of distinction between old (incandescent) and new (HID) technology in order to create a strong emotional reaction to the HID headlights and the cars they were associated to, which were typically in the high-end segment, thus falling in the luxury market category which is driven primarily by emotions (ego trip, social status, etc).
Sammi   [Tue 22 Jul 2025 at 17:59]
Nice little lampses Love
I did hear a comedian comment 'I stopped at a junction to give way to a street light', or summat similiar. Laughing
Max   [Wed 23 Jul 2025 at 08:34]
That's a good one! Is there any chances that heavy consumption of C₂H₆O was involved in that story? Wink
wide-lite 1000   [Mon 28 Jul 2025 at 04:10]
Interesting lamp ! I agree completely with having trouble differentiating between headlights and the streetlights when going thru the intersection on my way to work at 4:45 A.M.
Max   [Mon 28 Jul 2025 at 06:14]
Hopefully this problem will eventually be mitigated when more efficient colored (à la HPS/LPS) LED streetlights will be developed and used in the future. Spectrally, the broadband cool-white emission from current fluorescent LEDs is far from ideal, more lm/W could be squeezed out of the semi-conductor technology with a narrow-band emission spectrum featuring less blue and without the Stokes losses from the fluorescence conversion of light. There are still some technological hurdles that need to be overcome before we get such an efficient direct conversion of electrical energy into light (i.e., without phosphor), but I'm confident we'll eventually get there.
Maxim   [Mon 28 Jul 2025 at 14:33]
Great presentation as always, Max. Your photos were very much missed over on L-G, so I made an account here to compensate for that loss. Very Happy
Max   [Mon 28 Jul 2025 at 17:30]
Thank you and welcome to T-L, Maxim! I hope you'll enjoy the posts (many more will come), they are oriented towards quality here.

Comment 1 to 9 of 9
Page: 1