When I was searching about Powerlite I came across a list of tradmarks owned by Powerlite. One of these was "SpherePak" could this be it. Judging by the pole design I'd say that it is a Powerlite fixture though.
There are some PowerLite fixtures in my area with similar poles. However they have a sort of cylinder-shaped head with the bottom half being the refractor, and they are mercury!
Nope, those in my area are not tapered like the one you linked. They look like cylinders cut in half, the bottom half if the refractor and the other half is the fixture itself.
I'll have to take a pic of them. When I have a chance I'll get there and take a pic. I know a few of the fixtures are HPS (or have HPS retrofits), the rest are mercury with lamps of different ages.