150w light = About 15,000 lumens
250w light = About 25,000 lumens

Quick 'n dirty guide

Less than 2,000 lumens per sq. ft. --Not enough
2,000-3,000 lumens per sq. ft. -- Lousy grow
3,000-4,000 lumens per sq. ft. -- Mediocre grow
4,000-5,000 lumens per sq. ft. -- Good grow
Over 5,000 lumens per sq. ft. -- Excellent grow

A 150w will be enough for about 3 sq. ft. of an excellent grow. That's two plants in an area of about 15 x 29...which is fine. Like others are saying, $100 is going to be tough...$150 shouldn't be a problem though. This is just a personal opinion, but I'd go for a 250w for a quite a few reasons.

First, more light. You've got space for more plants, and it's a drag to have throw out a plant because you don't have light to flower it.

Second is the separate ballast. I've never seen a 150w HPS with a separate ballast. the ballasts get hot, and that results in a lot of heat in your grow area. Personally, I don't think a 250w light with the ballast outside the grow area produces any more heat than a 150w light with a built-in ballast. So you get more light with no more heat in your grow area.

Third--bulb availability and switchability. 250w HPS bulbs are a lot more common than 150w. They don't cost much more. You can more different types of bulbs. And you can more easily find conversion bulbs if you ever want to use a 250w MH for vegging.

Fourth--overall cost and efficiency. There's pretty much no difference in cost between a 150w and 250w system. And 250w bulbs are about 5-15% more efficient than 150w bulbs. Much more bang for your buck with a 250w.
Roughrider Reviewed by Roughrider on . HID lighting question! I was thinking about purchasing a 150 watt HID light and wondering if i can use that for vegging and flowering or do i need separate lighting for each phase. I am currently only growing 1 plant and might be planting another in a 4'x5'x7' closet. Any lighting suggestions for under 100$ would be greatly appreciated! I have looked at the el cheapo lighting guide and i am still confused on how much lighting i need for just 1 or 2 plants. Rating: 5