I think you can use it. The 250watt is a maximum value that the ballast
should be used up to not the value it works at. The output is always
determined by the load on it. A 150watt load means the ballast works at
150watt. You can't give out 250watts. 250 watts is the voltage
multiplied by the current. The current being determined by the load, the
lamp.
Hope that helps,
Chris.

Nick Wise wrote:

Can a 175 watt bulb be used in a 250 watt ballast?