I've been a member here for 6 years now and I see lots of people discussing older HPS or MH fixtures believing that they must've been originally MV and were converted to MH or HPS . Not always the case . I've seen several instances of 60's fixtures which were available in MH and HPS also .  For example , LM Unistyle 400 & Unistyle 1000 were available from the factory in all 3 flavors . The M-400A was also .  Mid 60's Revere catalogs list both MV and "Metallic Additive" versions .

 I've seen some of which more are originally HPS than MV , i.e. AEL 25 , LM Unidoors , M-400A .

I think that assumption comes from the dominance of mercury vapor back then...I've also seen old catalogs mention HPS and MH options too.

@BT25 - Yep, that's how I think too. Especially if the light doesn't have a NEMA tag.

For city streets I base the light source of the light on the lights that surround it. An AE 113 surrounded by other M-250R2s that are HPS? Must be HPS. A Westinghouse OV-25 in a city that I know has mostly GE lights that are HPS and I've never seen it before? Must be MV (I've seen this a few times). Of course you should gather info on whether the lights are city-owned or utility owned, and whether or not they've retrofitted lights, and of course what lights they've bought and their light sources; this also applies to private property too.

For shopping centers/strip malls/malls, it's hard to tell, since unless you've seen the inside of the light and the catalog number, you can't tell if they're original or not. Private owners are also more likely to retrofit their lights, unlike city/government entities. Of course, if the light has a NEMA tag, then that makes your job of determining the light source easier.

Exactly what I was thinking guys . Plus , a lot of older fixtures had long enough production runs to have been made in multiple lamp types (Silverliners , M-400A , M-1000) As for NEMA tags , even they can be replaced so as mentioned above , unless one physically sees the original label inside , there's really no way to tell unless the fixture in question pre-dates MH or HPS such as a clamshell .

In my area a lot of the older lights from the mid 70s onwards were factory HPS, before the advent of LED there was stuff like Unidors, OV-15s, and B2255s which were factory HPS. There were some older lights such as Unistyles and M-400s, those were more likely to be factory MV here.

The oldest HPS install here was from 1967, it used GE M-400As.

I have an ITT 13 that was MV with a yardblaster ballast when I got it... I can see evedence of where a NEMA tag once was, and I strongly suspect that it was originally HPS...