I know that the V and U mean vertical and universal, but what is the MA and MB? I heard something about arc tube material but now I am just confused.

Also, I have a 100W mercury vapor lamp that seems to operate as normal, but it has coated arc tube ends (like metal halide), but instead of a white coating, it is a shiny metallic coating. The coating is definitely on the outside of the arc tube. Is this normal? I haven’t seen any pictures on here of arc tubes that look like this (or maybe I haven’t looked hard enough). This lamp also doesn’t have MA/V or MB/U etched on it. Is there any other way to tell by the construction? Sorry I don’t have a picture right now but I might add a picture in the comments if you need it.

Thanks!
 

The problem is medium pressure MV lamps (MA/V), is that their arctubes are made from hard glass which can't withstand the heat of an arc bowing upward when the lamp burning horizontally and would be melt.
With high pressure MV lamps (MB/U), the quartz arctube can withstand the heat of an arc bowing upward in the horizontal position.

Wow, who’s idea was it to make an HID arc tube out of glass? These lamps are compatible with the same ballasts, right?

So if MA/V tubes are made out of glass, would they still have the molybdenum foil seal or just a wire feed-through? This would make it easy to tell them apart if this is the case.

Any ideas about the metallic coating on the ends of the discharge tube though?

MA/V have colder discharge, so they can have hardglass arctube when burned vertically. But when burned horizontally, the bowing arc get closer to the arctube wall, and may melt it.

Wow, who’s idea was it to make an HID arc tube out of glass? These lamps are compatible with the same ballasts, right?

So if MA/V tubes are made out of glass, would they still have the molybdenum foil seal or just a wire feed-through? This would make it easy to tell them apart if this is the case.

Any ideas about the metallic coating on the ends of the discharge tube though?

Quartz material was expensive at that time. Also, quartz melts at extremely high temperature and is hard to work with, requiring specialized tools and fuel like hydrogen burners. Also, it is hard to make vacuum tight quartz-to metal seal, due to very low coefficient of expansion. Molybdenum foil lead-in technology for quartz was not yet invented.

Hard glass of MA lamps range has more regular COE, so it is ready to make a stable seal with COE compatible molybdenum wire.

Metal (platinum) coating at tube ends means heat sparing just like modern zirconia (white) or rarely chromium trioxide (green).

Read a nice write-up by James on these lamps: http://lamptech.co.uk/Documents/M8%20MA.htm

First of all for clarification:
MA/V M: Mercury  A: Medium pressure design V vertical burning position
This is the trade-name introduced by Osram GEC
These lamps use a Borosilicate or Hardglass arctube and will be referred as medium pressure mercury lamps

MB/U
M: Mercury:
B: designation for a high pressure lamp
U: for universal Burning position.
This was also a trade name introduced by GEC.
These lamps feature a quartz glass arc-tube and will be referred as high pressure mercury or HPM lamps.


Yes, Roman is correct. Basically quartz was way to expensive when mercury lamps become popular. Only with the development of more modern technologies the benefits of the quartz arc-tube could be fully use advantage of at reasonable price. However quartz was used early on on small wattage ones as the efficiency of medium pressure lamps decreases with their power rating.
However one small correction: Quartz is also amorph, so a glass not a ceramic (crystaline structure). Hard Glass or Borosilicate glass is quartz with extra boon trioxide added.

The idea of using glass instead of ceramics was due to practicability. Sealing ceramics at these temperature and producing translucent ceramics is way more difficult then using glass which is one of the reason lamps using these material for discharge tube become popular some 20-20 years later.
Regarding compatibility, that is difficult. In continental Europe lamps used to be rated by there light outbut wihich gave us medium pressure mercury lamps with odd wattages like 450W or 265W, in russia 500W. These lamp have other characteristics then 250W and 400W HPM lamps. British lamp were rated however 250W and 400W were medium and high pressure lamps were compatible, with even special high pressure lamps being offered as tubular drop in replacements.
In the US to ma knowledge both 400W lamp are interchangeable. The 250W H-2 Lamp is however not interchangeable with the 250W HPM lamp as the first is designed to run on a low voltage.

Ahh I see, so different pressures can make different arc characteristics.

Yes, Medium-Pressure Mercury (MA/V) and High-pressure Mercury (MB/U). Coated High Pressure Mercury is MBF/U.