just wanted to add that more is not always better, and yes, you can have too much light sometimes.. i'm not saying that adding a 150 hps to your grow is going to be too much light, but say you've got a 1k light and only a 2 x 2 area or so, than it would be too much light for what space is there..
but so long as you've got enough space that is going to be able to benefit from more light, and your temps aren't going to get all out of whack, by all means add more light..