These compact fluorescent CFL helix spiral energy savers use an extra thin T2 mini sized tube, making them more efficient & extra-compact. Features a ES-E27 Edison screw (27mm) base/cap.They make use of special technology to start faster and their smaller size means that they give off a more concentrated light; making them a much better replacement for traditional light bulbs than older energy savers. Not suitable for dimming.Need more help in choosing a suitable light bulb? Read our guide Choosing Compact Fluorescent Lamps