Bulb Wattage unknown

Hi guys,
I've been given a metal halide balast and bulb. It looks like one of those industrial jobs with a built in balast. Problem is I can't find any refrence to power/wattage on the balast or the bulb? I'm guessing its 400 or 600 watt. Can I tell the wattage by the size of the bulb alone?
Thanks in advance.
peace.
Rufus.

I don't think, you can judge it by size. Maybe ask on Indoor forum?