As it pertains to our project, could someone tell me the differences
between using High Pressure Sodium lighting and Metal Halide lighting?

Thanks.

everyone here uses metal halide bulb

some people use a metal halide bulb that can run off a high pressure sodium ballast (read ushio)

i think a true high pressure sodium bulb is very yellow in color

What't the cheapest people are getting the Ushio bulbs for? There's a used quad tap HPS highbay light at work that I could use as long as the bulb doesnt' cost as much as a whole metal halide setup.

High Pressure Sodium bulbs give a narrow spectrum light, with a lot of orange and not a lot else.

They work in a relatively simular way to Metal Halide bulbs, but with a slightly different current, which is why 400W HPS ballasts are nearly the same but not quite as MH ballasts.

If the highbay fixtures uses an ANSI S51 ballast, then it would make a usable source for a ballast and socket for the S400DD lamp. Otherwise, it's virtually useless for a projector.

Certainly a magnetic ballast is cheaper than the eballast.

HPS lamps are useless for a projector, however. They just don't have the ability to show colour well enough.

So what's the cheapest anyone has found the S400DD?

LL store. They're $20 more, and special order at any of the local shops I found that would even admit that they exist.