NICE! The 100V 150W HPS lamps aren't common, especially in BT shape! weren't the 100V 150W HPS lamps the only BT28 shaped HPS lamps?

Is this seriously BT28 shape? Cool!

Yep!!

Nice! I believe some lower wattage HPS retrofit lamps are also made in BT-28.

Oh yep. I forgot the 150W retrofit HPS lamps were BT28 too. I guess only the specialty HPS lamps were BT28, probably to distinguish them from the "standard" HPS lamps. The 360W HPS lamps were (and still are IIRC) BT37 but i think those were the only BT37 HPS lamps. The 200W+ lamps were alwats the ET shape (except the coated ones which were probably either ED or BT37)

I've seen a coated 400w BT-37 HPS before. Not sure about other coated HPS wattages though.

the low wattage coated HPS were BT25 like the clear ones. I've seen the on ebay, actually, i think from your links.

Thing is..not sure why anyone would run a HPS lamp on a MH ballast (not that I'm concerned really). But I need to know, this 100V 150w HPS lamp is a conversion lamp?

no, this is a 100V 150W HPS lamp that is designed to operate on 100V 150W HPS ballasts (as opposed to a 55V 150W HPS lamp and ballast). They're both standard products but 55V HPS lamps and ballasts are far more common. The difference is that with 100V HPS ballasts and lamps, the 200-400W HPS igniters can be used. also with 240V line voltage, a reactor an be used for 100V 150W HPS whereas with 55V HPS that couldn't happen. On the flip side, on 120V line voltage a 55V HPS can be operated with a reactor (since reactors chop the line voltage in half).

so depending on your line voltage it's easier to use one over the other but 55V 150W HPS is much more common. I think the use of 100V 150W HPS has declined over the years but I have no evidence of that. It just seems like you don't see any 100V 150W HPS out there now... and no the lamps aren't interchangeable either. 55V 150W HPS won't work on a 100V ballast and vis-versa

Interesting, thanks. Now, except for the ANSI ballast code, which to me, indicates the lamp watts, how would one discern the difference between a 55v and 100v lamp? What markings do I look for?

You'd either have to read the lamp etch or the fixture label (55V 150W HPS is S55 and 100V 150W HPS is S56). Other than that i don't think you can easily tell so that's probably why the 100V lamps were BT28 instead of BT25. I'm not sure, but maybe the newer 100V 150W HPS are ED28 instead of ED23.5? I've never seen a non-BT28 100V 150W HPS lamp so i don't know...

Is 150W HPS the only wattage offered in 2 different voltages?

I think so.

I've heard the European HPS and MHs run on the same ballasts not sure if that's true of all of them though

IIRC European 70w HPS lamps (100v arctube) will run almost to spec on North American 70w PSMH ballasts and vice versa.

Ahh yeah i don't know about European lamps but 150W HPS is the only North American lamp offered with two voltages. Are HPS lamps the only lamps that are different in the UK versus NA?

I believe the MHs are different too, as probe start is rare in Europe. I think most MH ballasts there have a ignitor instead. The 1kW mercs are also different, ours usually need 400v OCV to strike while the ones in Europe are designed for operation on 240v choke ballasts.

I thought all mercs ran at 130V OCV? our MH has igniters too. Do they just call them "metal halide" isntead of "pulse start metal halide"?

Yeah, most mercs run on 100v except the 700 and 1kW which need 200v and the special lo-volt merc which only needs 55v. I believe the latter ran nicely on S55 (150w HPS) ballasts.