So I have a Westinghouse OV-15 that I am restoring. I want a light source that is crisp and white (not like /DX mercury vapor or anything like that) but not too bright and so I stuck a 70w metal halide ballast in it along with a Plusrite 70w mogul base metal halide. I decided to try it with the refractor indoors. It looked very nice, but I noticed that it appeared abnormally bright. It was definitely brighter than a 175w mercury vapor and almost appeared as bright as my 250w PSMH lamp. Is this just an illusion, or could there be something wrong with the ballast? I know for a fact that 70w metal halide is not brighter than a 175w merc. The lamp didn't appear overdriven or anything like that either. I am planning on getting a lux meter soon and so I can measure it to make sure it is at the normal rated output (around 5600 lumens) and compare it to a 175w mercury vapor, but until then, is a 70w metal halide supposed to appear blinding bright when new? With the refractor on the light it appeared brighter than a 100w HPS lamp even.

Is this a QMH or a CMH lamp? What is the ANSI code of the ballast?

Is this a QMH or a CMH lamp? What is the ANSI code of the ballast?

Quartz metal halide, M98 ballast. This is the lamp I am using.
https://www.1000bulbs.com/product/5030/MH-007007.html
(and yes, I left that review.)

Looks like the bright light is just an illution. The lamp and the ballast are compatible. I've a tracklight with an Osram HQI-TS 70W/WDL Excellence, which looks very strong and bright, despite it is much less glaring than the former 2xF54T5/865 chinese fixture that were before, and causes me much less headache (Only when I feel asleep, I've see its light being too strong for me).

The smaller light source may illuminate smaller areas on the emitting surface, basically same effect as with LEDs and lens panels. If you want to compare lightg levels, you gotta do it on illuminated surfaces without the light itself in sight, or use a meter

Lux meter measures Luxes, not Lumens. You cannot convert without knowing precisely the luminaire distribution or efficacy... Which you probably dont. It might be more straightforward to measure the bare lamp instead