An electronic ballast should draw pretty close to its advertised amount 250W. 
Magnetic on the other hand:
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					Originally Posted by  StirCrazy
					 
				 
				a M80 ballast (true magnetic M80) which is only made by Advance transformers (north american company) should be pulling around 400 watts with a 250 watt SE bulb a little less with a DE bulb, at 310 watts I would say they put a M80 starter and capacitor on a pulse start ballast and used that.  will be a little lower output this way (well a fair bit actualy) I am not saying thats what they did but I have seen that done.  the other thing I saw once was a european ballast converted to NA voltage (easy to do) this gives different out put as they are not a HQI ballast but are simular.  
  
Steve 
			
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 The full discussion is here: 
http://www.canreef.com/vbulletin/sho...ht=hqi+ballast
I'm not trying to sound like a jerk or anything. I just wanted to point it out because some people really go out of their way to try and find these ballasts which are no longer produced.