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MB/U 250W Mercury Vapour

MB/U 250W Mercury Vapour

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These 2 mercury vapour lamps have "frosted" arc tubes. The upper most lamp is badged "Altas" and I think is from 1975 but maybe earlier. The lower lamp is badged Thorn and looks like manufactured in 1984. I don't think Thorn had this lamp in their catalogue by the 1980s so don't know if it is badged Thorn and manufactured by someone else. There are certainly signs the Thorn lamp was cheaper to make, other than a very uniform frosting on the Thorn arc tube the Atlas lamp looks better made.

xenon_trig.jpg SON_T35W.JPG mb_u250w.jpg XBO3.jpg

Light Information

Light Information

Manufacturer:Thorn
Model Reference:MB/U
Lamp
Lamp Type:Mercury Vapour
Electrical
Wattage:250

File information

File information

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Filename:mb_u250w.jpg
Album name:tuopeek / High Pressure Lamps
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Date added:Jan 08, 2018
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merc
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Jan 08, 2018 at 03:41 PM Author: merc
Beautiful lamps!

Not a misoLEDist...

sailormoon_01_uk
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Jan 08, 2018 at 05:34 PM Author: sailormoon_01_uk
The Atlas MB/U Lamp has date code 14 which = to February 1967,

The Thorn Lamp looks like it's Philips Made as it has the same supports as the early HPI-T Lamps, anyway can you give the 2 digit number on the Thorn Lamp and I can date it for you, It's normally the two numbers between MADE IN (--) GT BRITAIN.




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Jan 08, 2018 at 06:45 PM Author:
They're certainly lovely lamps, I have the GEC one which is really good to see lit up
tuopeek
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tuopeek 111967450636623837217 tuopeek1 77334065@N05/
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Jan 09, 2018 at 11:35 AM Author: tuopeek
The date code on the Thorn lamp I think is 30. I bought it new in the mid 80s so 1984 looks possible but I have a Thorn 1978 lighting catalogue and it doesn't mention MB/U lamps but I guess it could be a 1976 date code. Interesting the Atlas is older than I thought but that would fit as the Atlas logo kind of dwindled in the 70s being replaced by Thorn logos.
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Jan 09, 2018 at 11:41 AM Author: Danny
Love these lamps with the frosted Arc tube. I have one knocking about somewhere . This has tempted me to dig it out and light it
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Jan 09, 2018 at 12:52 PM Author: sailormoon_01_uk
your Thorn MB/U with 30 on it = June 1984, as the 1976 MB/U is the same as the Atlas and Mazda MB/U lamps in Construction, it could be for Special Order as although MB/U lamps are No longer made, they are still available for the Military, NATO stock No 6240-99-996-6758 or 6240-99-996-6762 (250w MB/U) and NATO Stock No 6240-99-996-6771 (400w MB/U), but are now made by Iwasaki Lighting ref No HT250 and HT400 see the bottom of the page https://www.eye.co.jp/documents/en/lighting/sources/mercury/p50.pdf.
tuopeek
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tuopeek 111967450636623837217 tuopeek1 77334065@N05/
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Jan 09, 2018 at 01:07 PM Author: tuopeek
Interesting
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Sep 11, 2018 at 10:35 AM Author: Cal
1984 seems late for one of these. I also have the atlas with the frosted arc tube, in 400W.
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SodiumVapor 105843202020668111118 UCpGClK_9OH8N4QkD1fp-jNw majorpayne1226
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Sep 11, 2018 at 02:17 PM Author: HomeBrewLamps
Why frosted arctube? Seems like that would bring down efficiency a bit.. And not prevent glare.. Why not frost the outter envelope instead??

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tuopeek
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tuopeek 111967450636623837217 tuopeek1 77334065@N05/
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Sep 12, 2018 at 02:59 AM Author: tuopeek
Not sure is the short answer, It just seem to be these mid sized lamps that got this treatment and not all of them. Interestingly the low wattage ones often had the outer frosted as you suggest.




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Sep 13, 2018 at 08:56 AM Author:
The reason for clear tubular lamps is so that the arc tube is in the prime position for the optics of the lantern. With diffuse outer bulbs, the entire surface of the lamp is the light source, so it is more difficult to get good light distribution. For low wattage lamps, where the luminaire tends to be lower down, this isn't so much of a problem, but with tall columns on main road lighting, it's more important to get good optical control.

Why the arc tube is frosted on these lamps is unclear, I'm sure someone like James will know.
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Sep 13, 2018 at 09:09 AM Author: arcblue
I had one of these frosted arc tube lamps but gave it to another collector. What I was told was the reason for the frosted arc tube is that these lamps were designed to replace MA/V lamps with glass arc tubes and the frosting diffuses the arc so it is more like the wider arc of the MA/V lamp.

I'm lampin...





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Sep 13, 2018 at 09:17 AM Author:

I had one of these frosted arc tube lamps but gave it to another collector. What I was told was the reason for the frosted arc tube is that these lamps were designed to replace MA/V lamps with glass arc tubes and the frosting diffuses the arc so it is more like the wider arc of the MA/V lamp.

That's a possibility, they do look a similar physical size to MA lamps.
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Sep 13, 2018 at 09:17 AM Author: Cal
Tbf I thought all tubular clear mercury lamps were retrofit for MA/V as they made them way after the elliptical lamps became common.




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Sep 13, 2018 at 09:26 AM Author:

Tbf I thought all tubular clear mercury lamps were retrofit for MA/V as they made them way after the elliptical lamps became common.

Possibly, but the early MB lamps tended to be the same physical size as the old MA ones, in order to fit the same lanterns. They became smaller after a while, I have a GEC 250W MB/U from 1972 that's about half the size of these:

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Sep 13, 2018 at 11:47 AM Author: Cal
Relative to the cap the arc tube is in virtually the same place though. The space at the top was just dead space that could likely be removed saving on production costs. I have the atlas 400W with this frosted arc tube and it is to be honest unecessarily long, but as you can see the later variants of the lamps tended to be shorter. I can't see any reason for them to be produced well into the 80s except for accurate retrofit into the likes of GEC Dioptron lanterns, which were specifically designed for medium pressure lamps.
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