Pity it ain't one of those special "Marks and Spencer" ones! I have two of these, both used bit operable, they look Identical. I think this is tri-salt if I recall correctly.

These sodium-scandium lamps were developed together with Sylvania in the US IIRC, and while they had outstanding colour stability throughout their lives and a high intitial luminous flux, they suffered from quite a large lumen depreciation early on which made them less efficient towards the end compared with its rivals.

Hi Mark,

A fellow Enginneer/Collector used to use these in the Dedicated Integral Geared Thorn Alpha 3 Street Lights in Derby City Centre, anyway the Date Code 71 = November 1979. I too have some of these in Base Up to Horizontal and Horizontal, I also have 2 x 400 watt and 2 x 1000 watt Clear versions Base Down Only for use in Lighthouses.

I really don't know what made me sat "Tri-Salt".....maybe I was thinking of the Philips HPI-BUS lamp....because when I got these, I did fire them up and check the spectrum, I now recall I was surprised to see a scandium spectrum, one of the few non-American lamps made at that time to exhibit it. Actually it was one of only a few British Metal Halides full stop!

Colin. have you posted pictures of your two clear versions already?


Oh, one more thing...does anybody know what the "B" signifies.....mine both have a lone capital letter too, but I recall it was an "R", I may be wrong though.

What would the date of that 250w that I uploaded be with a code of 70?

"70" = October 1979,1987, 1995 Etc.

Yep the 250 watt lamp is dated October 1979 if 1987 it would be in a blue sleeve with Thorn EMI if 1995 it would be in a purple sleeve and would be a GE lamp.

Cheers.

H Mark, No Problems glad to help Identify your Lamps

Hi Globecollector to see my Clear Metal Halides can be seen HERE for the Thorn 1000w MBI/BD, see HERE for the Thorn 400w MBI/BD see HERE[/url for New Old Stock Thorn 400w MBI/BD Lamp and see [url=http://www.lighting-gallery.net/gallery/displayimage.php?pos=-117972]HERE for a Used Thorn 1000w MBI/BD lighthouse Lamp.