Here are a couple of pictures showing the old high-bay fixtures in my high school's gym that I took from a couple of old yearbooks. This gym was completed in 1966, and I'm pretty sure these are the original fixtures (the oldest photo is from 1975 or '76). I the first one you can clearly see what looks like ballast boxes and steel electrical conduit connecting to the fixtures. These fixtures were late replaced with 400W metal halides, probably in the 1990s.

I assume these were mercury vapor fixtures, but I don't know. Can anyone identify the make and/or model, or know of pictures of similar fixtures on this forum or elsewhere?

I was born after the peak MV era, but I distinctly remember when 400W MH was the most common gym light fixture. Were MV high bays commonly used in gyms before the MH era, and if so, what was the wattage? If not, what was common? I'm guessing 400W MH indoor high bays became common in the 1980s, and probably replaced similar 1000W MV fixtures, but I don't know.

As far as I know, I believe mercury vapor fixtures were commonly used in gymnasium lighting prior to metal halide becoming popular in North America. This can be evident because I have read that there were type T self-extinguishing mercury vapor lamps being made in addition to type T self-extinguishing probe start metal halide lamps since I recall reading that some lawsuits arose in the 1970s over errant balls striking lamps and shattering their envelopes and causing sunburns on spectators and athletes due to the lamps emitting shortwave ultraviolet radiation from the bare arc tube.

I am also sure that some gymnasiums also used mercury vapor high bay fixtures in conjunction with incandescent high bay fixtures to provide decently color accurate lighting at high efficiency before phosphor coated mercury vapor and metal halide became popular.

Over at my high school, I recall that my gymnasium had some 200-300W incandescent Holophane LoBay fixtures that appeared to have mainly been installed for possibly providing color correction for former mercury vapor high bay fixtures since at the time I was a student, I recall F32T8 fluorescent high bay fixtures being in use at the time, but saw old photographs showing round HID high bay fixtures. I have been thinking they were probably mercury vapor as evidenced by the presence of incandescent fixtures throughout the gym.

In fact, some collectors do own some mercury vapor Holophane ELB high bay fixtures with a ball guard, which indicates they were possibly used for gymnasium lighting:

https://www.lighting-gallery.net/gallery/displayimage.php?album=search&cat=0&pos=20&pid=263334

https://www.lighting-gallery.net/gallery/displayimage.php?album=search&cat=0&pos=25&pid=259581