I heard of that as well, the full spectrum lamps lose their K rating over time, but forgot how long to let them run before replacing them. Based on what OFL recommends, every 12 months or so, I'll swap it out with a new one, but I'll keep the "used bulb" around for the basement or something.
I'll run mine on a automated timer for about 10 hours a day, from 5pm-5am. [Tanks will double as a nightlight] I may let them run for 4000 hours before I replace them with a new bulb.
I heard it was like replace every 6 months for reptiles. But those are basking UVB or something lamps