[fkshiu]

http://www.hiddenreef.ca/storefront/...&categoryid=35

http://www.lightrail3.com/

http://www.drsfostersmith.com/Produc...&N=2004+113356

http://www.homeharvest.com/lightmovers.htm

It more accurately simulates the sun passing over your tank as the day goes by and you can get away with fewer MHs (only 1 is needed over a 4' tank, for example).