How large is the area that you wish to light? HID (metal halide and HPS) can be tricky for starting seeds because they don't evenly illuminate a wide area. Stuff in the middle may fry while stuff at the edges will lean and stretch. The area you wish to light will also determine how much power you need. A 400W HID will be good for at least ten square feet, possibly double that. Small HID lamps tend to be less efficient and it probably isn't worth using less than 250W. Also, older lamps are less efficient and you might be better with a new fluorescent or compact fluorescent. How long do you want to grow them under lights? Do you have any natural light at all?

HPS light is the best as a supplemental light, simply because you get the most light for your money/electricity. As the only light, it usually needs extra blue spectrum to produce healthy growth. You could get an enhanced HPS (extra blue from an HPS bulb), add some blue-ish fluorescent tubes, or many people just use metal halides to keep it simple.

Fluorescents generally need to be almost in contact with sun-loving seedlings to produce good growth. Good ventilation is also helpful to keep temperatures down and have some moving air around the seedlings. A modern four-tube setup should be well up to the task, older T12s or magnetic ballast lights just might not be intense enough. Look for 48" T8s producing around 3,000 lumens, they will grow good seedlings. Overdriven lamps or T5s will produce even more intense light.

Ceramic metal halide is the way to go...Best of both worlds. I kinda feel like a pioneer here. Once people see how wonderful these lights perform they'll never turn back. I'm not talking about if your just starting seeds for transplant outside, then flourecent is fine but, if you want to grow vegies or whatever indoors, to maturity, these lights are definately something you should consider. I'm doing eggplant, toms, hot pepper and bell pepper right now and am very impressed w/ this light.
(400w philips cmh w/ 4' vertizontal reflector)

Here is a link that might be useful: {{gwi:134681}}