Kind of a silly question...
 

I have a silly question for my brother-in laws tank. Would a 150 watt MH Ballast fire a 250 watt bulb? Im aking because i have a couple of bulbs kicking around, and he needs one until one of us can get into the city to pick up a new 150 watt bulb.

I don't know for sure but I don't think so...I think it will start up but not really run properly. I do know for sure running a 150 watt bulb on a 250 watt ballast doesn't work properly...the bulb burns out in a matter of days. Well mine did anyways when I tried it.

i dont know but im gona guess no it wont

It may fire, but it will be really dim, may as well use a 60w bulb.

I remember reading someone was successfully running a 250W bulb on a 150W electronic ballast.

I tried running 400s on a 250w electronic, next to no light. Maybe it's different with smaller wattages.

Never a good idea to try making electrical components that are not matched in their ratings work. Asking for trouble IMO. Best case insufficient light, worst case fire hazard or exploding bulb/ballast. I'd even stay away from the overdriven T5 setups some folks rave about. A lot more heat for a little more light.