I'm not sure how long they last but I've read they lose quite a bit of their intensity after 6 months to a year and should be replaced that often. On the other hand, I have a 25 watt Gamma that I've been using for almost 2 years and haven't replaced the bulb. Not because I doubt it needs to be replaced but because the idea of spending $40 for a new bulb is too painful, lol.