Really what do you think? Out of all the different wattages for a lamp which one seems to be lost your brain. Not asking about rarity per say, just persistence and memorability.

Hmm here's what I think:

MV - 75w, it always seemed like it was close enough for 100w so it played second fiddle to that.

HPS - either 200w or 250w. Again very close power ratings. I know the 250w came first and the 200w was later developed as a lumen match for 400w MV. That or some of the wattages between 400w and 1kW that exist but wasn't common for general lighting. 

MH - Hmm hard to say, 50w and some of those later pulse start wattages are rather forgettable for me.

INC - probably 50w or 75w. 50w was only common here in rough service and 75w lamps were never common in my part of Canada.

Well here's my view on this

MV-700w. Never knew they existed until I joined LG.
Also 50w, how often do you encounter those?
I believe there may have been a 40w lamp also, not sure about that.

HPS-35w and 50w. I don't think that the 35w was ever very common.

MH-35w and 50w. They seemed to have only been a fad used in display windows in malls back in the 90s and now all but forgotten.

INC-15w, 25w, and 40w. For the life of me I've never had a clue where you would use those. I'm referring to the "A" shape for all three.

Fluorescent-56w F72 T12. Not the most common in the world are they?

LPS-Any of them. LPS is the rarest light source that ever existed here in Florida.

Good point jamie, i do have a few responses for what i have seen.

In dodge city there is a second hand store that i think used to be a salon, it had F72 slimlines in rows near the back, most didn't work but it was still a great site.

H45/40w mv was really rare as it was considered too close to to H46/50w mv that 50w just became the standard and a lot of lamps at the time where printed with 40/50w before just being called 50. I think people forget about H43/75w mv as it was a bit too close to 100w and never caught on like 100 or 50 did.

15-40w a shaped incans never seemed to work, i think they where for lamps but everyone ended up using 60s anyway. I do use a 25w piano bulb for my table lamp though, works a treat.

You know Max when I think about it 75w MV may be even rarer than 40/50.
I remember seeing old lighting brochures from way back that 40/50w MV was intended for post lamps for residential frontyards.
But sitting here thinking about it I'm not sure if I've ever heard of 75w MV.

Interesting what you said about the F72s not working because everytime I encounter them same thing.
Right now I only know of 2 places that have working F72 T12 fixtures, my kitchen and an old hardware store in an obscure part of town.
Of course I had to replace the ballasts in both of the F72 fixtures in my kitchen.

I always saw F72 as the light in the corner where a F48 was too short and they couldn't get a F96 in there. I think thats why it stayed so uncommon, but the goverment bans did get around 6 foot lamps due to there forgetfulness i think.

I think for hps it's definitely 310w. My reasoning is that since 700w was sorta uncommon its hps replacement also was, and the lamps where always harder to find than the 400w versions, that was the popular one. 750w hps was also pretty uncommon, i was unaware of its existence until a few months back.

Oh shoot! You got me on that 750w HPS!
I think I remember reading something about it but that's all it is just a vague memory.

Yeah I also agree about the 310 HPS. That's an unusual one. Don't see the point since 400w equipment was ridiculously common.

And yeah I think that's probably what an F72 is for. A quick solution when an F48 or an F96 just won't work.

Actually , 310 HPS is really really common here . Just about every highway in Ohio has 310w HPS somewhere on it .
 
 Uncommon for me it's MH : all of those strange Venture Pulse start wattages !
                      MV : 40w Yes , it existed ! Most lamp manufacturers had 40 & 50w as the same lamp but with a different               
                           ballast. Also don't forget about those weird linear shaped 3,000w MV's .
                     HPS : The 750w

I think the supposed 125 and 175 watt HPS were strange, when I think of those wattages I think of the more common 175 and 125 watt MV lamps.

Don't forget the really early 275 watt HPS !!

What about H40/425w MV?

Didn't even know that existed until it was mentioned here a few months ago .

From all available MV lamp wattages the most uncommon was the 700W. All others seems to be very common including the 50W.

HPS it would be the 35W which Osram was offering in the 1990s. Never seen one though.

For MH/ CMH lamps the 100W G12 was a very uncommon and short lived version.

The NA/ SOX 135W, 180W and 18W were quite uncommon wattages here.

On fluorescent lamps the 6ft 75/85W tubes were only used on refrigerators in super markets but unknown elsewhere. The VHO 110 and 160w were available here but I haben’t seen any. Only the 96” 215W PoverGrooves and T12 were quite common in the past.

Interesting how everyone's perspective is different.

40w MV was rolled into the 50w rating very early on in North America I think. In Japan they still had dedicated 40w MV lamps which I picked some up a few years ago. Another would be 80w over here, there was a yardlight that used that wattage but it never took off here. Same applies for 125w mercury in the US but it was used widely in Canada.

The odd grow lamp HPS wattages are rather uncommon for me. 750w I know as they're used in high mast lights here.

Anyway for the odd HPS wattages used in roadway lighting, it was to lumen match other sources. Some places chose to lumen match while some usually rounded to the nearest "normal" wattage.

200w = 400w MV
310w = 700w MV
750w = 1000w MH

The 33" 25w fluorescent is another oddball. It was apparently the longest lamp that could run off a 120v choke but seemed to have become uncommon. There's also the 31w F48T8 slimline which I think only Sylvania made.

Don't get me started on how many odd pulse start MH wattages are there, especially the almost proprietary Venture only ones. 

Speaking about fluorescent lamps there are many more which were very uncommon here. For example the 40W 2ft tubes which were used only in some places for street lighting but it’s very unclear to me how famous this lamp type was in the 1960s. The 16W 720mm T18 tube is also one example which I haven’t seen much in use but most of the hard ware shops are still selling these tubes even today! All U-Bent tubes were much less famous than in Germany for example.

The HPS 600W HO was also very uncommon here which normally found its place in high-bay lighting as a alternative to the less efficient 1000W rating.

Here in Switzerland there were no MV lamps available like 40W, 100W and 175W but the ominous 185W which I still haben’t seen any except of the ballast which runs these lamps.