This is an early 50w High Pressure Sodium lamp, it didn't even exist three years earlier. The arc tube is much larger than modern 50w arc tubes due to the large bore design. The large bore design requires heat shields at the ends of the arc tube for proper temperature control. Additionally, this lamp features the BT25 envelope, Sylvania eliminated this shape in 1981.
Yeah in 1981 Sylvania started using ED for all the lamps at 100 watt MV and all the HPS at 150 watt and below....the Sylvania's 80s ED 23.5 shape had a huge dimple! Until around 1989 or so they started with ET-23.5 shape!
Your mention of the larger burner diameter in this vintage Sylvania lamp is quite interesting. In the UK, the first 70W models develloped by Thorn in the early 1980s indeed featured a large bore discharge tube for reasons that, I think, were different from the motivations of Sylvania.
Thorn was faced with the problem of back-arcing which led a fast deterioration of the electrodes, and thus to a fast end blackening of the burner. For this reason, they used a larger burner diameter to limit the extent of end blackening and keep the lamp voltage rise over time as low as possible. In the case of Sylvania, I don't think they suffered the same back-arcing problems as Thorn did - it seems that the reason for the large bore burner is just a pragmatic design approach: They simply used the ceramic tubing employed for the 70W production until they could implement a properly designed 50W burner.
By the way, I have a later model of this 50W lamp; it has the rounded BT bulb the company used during the early 1980s and features smaller burner, which still features the heat-insulating metal bands strapped at the discharge tube's extremities.
Hi Max thanks for the explanation! So it features a 70w sized arc tube? I wonder if this lamp will be pretty dim. I have a 50w HPS streetlight, maybe its time to pull it out and fire up this lamp...
BTW, the rounded ET23.5 shape you mentioned came out in '88. Between '81 and '88 Sylvania used the ED23.5 envelope, just FYI.
Thanks for this information, I thought that Sylvania used this bulb shape much earlier. Does this mean that this lamp is from '92 rather than '82 then? what was the wrapper design at that time?
As for the size of this 50W burner, I think it only has the diameter of 70W discharge tubes, but its electrode distance should be shorter so as to maintain a proper wall load and temperature during full regime.
Yep that one is indeed '92. In '82, in addition to the ED23.5 envelope, the package would be blue with the shape of the bulb on the corners, also the base insulator would be the older rounded design. Sylvania went to the angled insulator in '86.
You really are an encyclopedia on the design features of American lamps that's good to know anyway, and I'll correct my database for the date codes - thanks!
Max are you talking about me or Dave I mentioned the ED shaped
Yes Dave knows a lot, but I learned a lot from HIM and from looking at lamps I get....I am always interested in "How old is that thing what changes was it made what features" blah blah.....
So it was 1988...I was pretty close...thought it was around 1989...
I have a Sylvania ED23.5 HPS lamp (100w) and an ET-shaped one....I've seen some streetlights with the BT-25's in them...didn't realize the lamps were from 1981 or earlier! I would love to find a 100w BT25 in working condition.
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Thorn was faced with the problem of back-arcing which led a fast deterioration of the electrodes, and thus to a fast end blackening of the burner. For this reason, they used a larger burner diameter to limit the extent of end blackening and keep the lamp voltage rise over time as low as possible. In the case of Sylvania, I don't think they suffered the same back-arcing problems as Thorn did - it seems that the reason for the large bore burner is just a pragmatic design approach: They simply used the ceramic tubing employed for the 70W production until they could implement a properly designed 50W burner.
By the way, I have a later model of this 50W lamp; it has the rounded BT bulb the company used during the early 1980s and features smaller burner, which still features the heat-insulating metal bands strapped at the discharge tube's extremities.
BTW, the rounded ET23.5 shape you mentioned came out in '88. Between '81 and '88 Sylvania used the ED23.5 envelope, just FYI.
As for the size of this 50W burner, I think it only has the diameter of 70W discharge tubes, but its electrode distance should be shorter so as to maintain a proper wall load and temperature during full regime.
Yes Dave knows a lot, but I learned a lot from HIM and from looking at lamps I get....I am always interested in "How old is that thing what changes was it made what features" blah blah.....
So it was 1988...I was pretty close...thought it was around 1989...