changing CFL bulbs

I was reading somewhere on someone else's thread while trying to learn about CFLs and he mentions dating the bulbs and changing themout because they lse strength after so long but he never really mentioned how long that e was wondering if anyone had any thoughts or comments on this it may be a newbie assumption to assume it last as long as the life of the bulb

after 6 to 8 months i would change the cfl....it loses its PAR output slowly but it does make a difference.

Okay thanks for quick reply glad no one said once a week

I bought my current CFL set up about 5-6 years ago, I said I would switch to better light system when the bulbs needed replacing. Original bulbs are still glowing nicely, getting fed up now cause I want a 400W HID or similar but know I wont upgrade until these go. Not that i cant afford it, just tight I reckon, or lazy, would have to re-work my grow room. They do say the light degrades over time but to be honest I have not noticed and no noticeable difference on yields.