250W HPS Ballast with 150W HPS light

pretty sure you can't bro.

for one.. it would be a fire hazard.

better safe than sorry. plus, it could destroy your ballast.. and or bulb.

that's why ppl choose what wattage they want.. before they purchase their light system.

You could always add a couple of CFL lights.. they work alright when in conjunction with MH/HPS lights.

Especially for side lighting.. CFL would be the way to go.. as far as adding watts to your grow area.

But then again, I have two 150watt HPS systems.. started out with one, then ordered another one. Which gives me a total of 300watts total.

Not sure how many lumens it would add.. I'd have to check the bulb specs.

That's another thing, you could add more (lumens not wattage) just by changing bulbs bro.. some bulbs (even same wattage bulbs) put out more lumens per watt.. than others do.

Hope that helped you out some.