I know our lfs has the 400watt on his tank and I just put the 250watts on my tank 5 days ago sothey have not burned in yet. So far they look the same to me, although he had some really nice light blue montis which I bought and brought them home and they had a little purple in them under my lights, if that tells you anything. I really like these bulbs and almost bought the reefluxs 10k but now I'm glad I didn't. I just don't understand why more people don't run them, maybe because they are so expensive and hard to find.