I've seen two different ballasts. which one is better?

[chubs]

They have HPS bulbs that are the normal socket size, but still need to be run by an s51 ballast.. these are cheaper than other ballasts ive seen, are these any different than the larger sized bulb ballasts that don't fit into a normal socket?

 

[TorturedSoul]

Bulbs or ballasts?

If you mean bulbs... I haven't run across HPS bulbs with bases sized for medium (household) sockets larger than 150-watt ones. Most HID bulbs are sized for a mogul (large) socket. That doesn't necessarily mean they don't exist. But it seems like you'll have more choices if you go with the mogul socket setup.

 

[chubs]

there's a 400W HPS at home depot by my place that fits a smaller socket, i didnt know if the size of the socket had anything to do with the power output.