I had 2 - 175w 12K's that were 14 months old when I last tested, one was at 95% and the other was at 100% brightness. Doesn't fit the typical MH burn out or depletion in brightness as other MH lamps. Although I just recently sold this tank I am keeping up with the current owner to see how long they will last before they need to be replaced. Going on 15 months.