there two models. one is just a timer/ ballast. the other (actual light cycle unit) has a built in auto dimmer that supposedly mimics sunrise to sunset. it takes about 1/2hr to ramp from 50%-100% i had one of the latter about a year ago, the biggest problem was reptisuns were still t-12 and the light cycle unit only went to t-10 so if you wanted to use it you had to use other bulbs so i sold it. now of course reptisuns are t-8 so they would have worked fine. another issue was the dimming, fluorescent bulbs do not dim all that well, and the unit doesnt start out at 0%, it starts out at 50%,now i didnt check things out with a uvb meter, but visually, what is supposedly 50% looks almost as bright as 100%, you couldnt really tell any significant difference between the 50%startup and full power. i thought the end caps fit fairly well , but the fairly heavy guage wires were unruly and had to be wire tied together and like an earlier poster said, there is no reflector,and the bulbs are really easy to break when not secured or mounted in a fixture. it might not be a bad setup if somebody wanted to build a really large cage and build the lights into the cage, but for a regular cham cage i think i prefer the double t-8 fixture with electronic ballast from home depot for $20 (2ft) or $30 (3ft) jmo