It doesn't need a ballast.... I thought all HID lights need a balast.
It needs a ballast. From the link:
The 200W rating, for use on an S66 ballast, is unique to the American market and was introduced primarily as a replacement for 400W mercury lamps, since it produces very nearly the same luminous flux.
Probably it's one of those little ballasts that's built into the fixture behind the reflector.
I have an old security/parking lot light, but I've always though the heat it puts out was a little to sketchy for a cabinet or closet and the metal enclosure is too rugged for me to cut out ventilation ports w/a Dremel.
I have taken them apart before, though, and basically used them as a kit. It's since been pointed out to me that there are easier ways of doing
that though.
Anyway, yes, there's a S66 ballast in there somewhere.
If you look in the product docs as quoted above you'll notice that it says that S66 / 200W HPS was introduced a while back as a replacement for older mercury lighting, and was only used in the USA. I think that might be problematic, as it appears this type of lamp and ballast is being phased out. Grainger has discontinued all of their S66 ballasts. I'm not sure how much longer you'll be able to buy replacement lamps.
But, hey, you can't beat free!