Interesting size difference. Lacking multiple taps does seem to make a difference!

I had to reverse the tray here, both ballasts, along with ignitors just wouldn’t fit!, that’s why the GF looks like it’s hanging off the edge!

You can get twin electronic 35 & 70 ballasts but I suppose 100 and 150's would be pushing it in a single package!

It’s also lumen output in here, 28,000 lumens from a 250 SON is uncomfortable to sit under for hours at a time, the heat is nice on winter days, but excessively bright! , 2 x 100 watt halide is bearable, but I normally run twin 70s, or a 250 merc which is also about nice!, this is also why you will never see any 400 watt halides or mercury on this rig as I use it for an everyday room light! , I have a 1 KW studio tungsten lamp too that has its own spot here, but that’s like having a collapsing star going super nova in the bloody room with you!

i do have a twin electronic ballast 35W and 70W as spare I could bring it to the meet if it is desired.

The Thorn ignitor looks like made by Sabir, France, because of the logo, design and the Made in E.C.

The ballast?, you could be right, I’m not sure who was making them for Thorn in the mid 90s?

The ballast is UK made, so it can't be Sabir, France. I think only the ignitor made by them. The ballast can well be made by Thorn themselves before GE takeover.

That's where the gutted low bay comes in handy, running it in uplighter mode really helps for those brighter lamps

The left hand ignitor is a VS Z400M, the right hand one is an SPL England CD-Z 400W

How you can run two 100W MH lamps with one ballast?

Have a look at the photo again Dor...

I don't see the other ballast.

I think I can see the confusion here, the other ballast is the top one with SHP 100 on it, you can’t really see it’s depth on the photo angle, which is why dor possibly mistook it for an ignitor, but it’s quite deep, but thin in width

It is way smaller than the Thorn UK ballast.

I expect a large chunk of the lower ballast is open space, you can see where the case is crimped onto the core which only comes to half way on the side!