6 months is correct but if you get a uvb meter you might get a year out of some some might come to you with low uvb brand new all depends but without meter 6 months
i use the arcadia d3 18 inch linear tube and i got them in december and they seem to be doing fine i read you dont have to replace them that soon i dont know the uv levels cause i dont have a solormeater or what ever there called