Is the purpose of the outer jacket to help keep in heat or cut UV in such a design? Interesting lamp though

Very nearly had the opportunity to obtain one of these from college a few years back, but they changed their mind at the last minute! Would think that the outer envelope would mainly have been for mechanical support and to act as a draught guard rather than providing any insulation as such. Know that there was an American lamp made which dispensed with the outer jacket entirely.

Cheers guys. Yep the MA arc tube doesn't require the same level of thermal insulation or indeed need to be sealed from the atmosphere hence the open seal design! Crompton were the only maker to adopt this method, was cheaper to produce and allowed them to compete with the big boys! The pads at the ends are asbestos and as a result, you can see asbestos dust inside! Another incentive to ensure this lamp doesn't break!

@Zel - Really!? No outer jacket!?

Yep, the H2 from GE. Can be seen on James' site.