Has anybody else ever noticed that on older fixtures that are now HPS (for example the OV-25), there's a small round thing protruding from the underside of the lamp, like right below where the photoeye would be if it was so equipped?  Is there something that has to be added to an HPS light that needs to be partially mounted external to the fixture?  I'll try to capture a photo of one next time I can, but most of the ones I've seen are on freeways where it's not practical to stop and take a picture.

Just curious what that is.  I'm wondering if the starter or cap has to be mounted outside for whatever reason.  Really strange.

It could be a level for mounting or ajusting the beam pattern,the starter would be able to fit inside.Are these full cut off fixtures?

It could be a level for mounting or ajusting the beam pattern,the starter would be able to fit inside.Are these full cut off fixtures?

Nope, these are regular drop lens lights.  I found one I can probably get a picture of from a bridge.  It'll have to wait a bit because we're just about to head out of town for a few days.  I'll get one up as soon as I can snap it.