They will WORK but not work as good as many other things, most flood lights are MH bulbs so i wouldnt try to flower with them, and most of them arn't to powerful to begin with so i wouldnt expect any surpriseing results, like i said they will WORK but not work as well as many other things...
if you're looking for a cheap way to grow to you could use cfls, which are the twisty looking bulbs that say energy saver all over the package. you can get them anywhere, home depot, wal mart, you name it. you just screw them in to normal light sockets, and you're in like flynn.