keep the light far away at first, then move to about 18 inches. Depending on the amount of heat. I have a Lumatek so i cant speak to the other brands, but so far it has been dependable. It has some cool features like if there is an outage, it has a fuse to protect the ballast against a blow out, and it has a feature that waits 15 minutes after an outage and turns on automatically.