I was about to mention the socket orientation! There is a position on the lamp socket bracket to have it that way, and early versions did have the lamp tubes over / under like this rather than side by side. The lamp support they came with was slightly shorter so the lamp sits level rather than at an angle. then there's the two positions for burning the lamp with the tubes side by side. I do wonder how those minute changes affect the light distribution

I knew one of you guy's in the field would have immediately spotted this had I not said anything!, I also never understood why Philips had the tube legs horizontal, the bowl in the MI was very similar optically to the Beta 5, albeit with slightly less side louvres in? But running the legs of the tube horizontal, in my opinion just encourages pools of sodium to collect like they did in the old SOs

It came from the MI50, the shape of the gear tray meant there wasn't room to put the lamp holder the other way around. It also meant that the lamp could be closer to the gear tray, so in theory slightly less upward light. That's pure guesswork on my part though. What wee need is a good room to do photometric tests and finally settle this debate. The whole over / under vs. side by side is a strange depate, as almost all lanterns have either one or the other and different bowls. The MI26 / 36 I think are the only ones that can have both, so would be perfect for testing if someone had the equipment to do it. There's also the debate of lamp socket at the street end or column end of the lantern, and if that made any meaningful difference as well

Yeah, I would guess, (going off the inverted gear tray), in the 26/36, Philips wanted to keep the lamp as high as possible to produce maximum downward light as you say.

I never thought of that as inverted, but now you mention it it is inverted compared to the likes of GEC.

Well, technically it's not a 'gear tray' on these as it's only got an earth wire attached to it , it's a bit like the tray in a 2600 maybe?

2600s have gear on the trays. My Z9464 90W diamond bowl GEC has the gear mounted to the canopy with the reflector underneath, so it's probably like that