And I hop on and confirm those responses.hps and MH need the large mogul sockets and a ballest that corresponds to the size bulb you wish to use.ie different size bulbs can t be used in different ballast setups.You cant use a 250 watt bulb in a 400 watt ballast or vice versa you cant use a 400 watt bulb in a 250 ballast.Gotta match them up.