MOGUL is the screw-base size ...it looks like a conventional bulb, but is much larger ... you also need a ballast for these lights , gets pricey ... go here for the best prices I've run across ... I have ordered other items from them, and received fast service ... http://www.hydroponics.net/grow-lights.asp ... be sure to surf their site thoroughly, they do have very handy items ... :thumbsup: