The Lumatek Dimmable 600W ballast. This ballast features a dimmer switch which allows you to reduce the power pack from a 600W to 400W power pack if heat becomes a problem. Also has the super lumens switch in order to increase power. Improves energy efficiency while hardening off. Reduce the light and heat output from your lamp. Four settings 360W, 400W, 600W and Super Lumens. Use either a 600W or 400W lamp.