T5 HO Bulbs - How often do you have to Replace them? I hear many Different Opinions

How often do you have to Replace T5 High Output Bulbs?



I hear so many things from so many people.



6 Months

9 Months

12 Months



I hear that it depends on the Fixture - For instance if you have a top of the line ATI Fixture you can go 12 Months but any other Normal Fixture you need to Replace the Bulbs every 6 Months.



My LFS says that at the One Year Mark the Bulb will retain 95% of its Original Intensity and will Drop off quickly after 12 Months so you do it every 12 Months.



Others have told me that the Bulbs start loosing intensity from Day 1 and it is Downhill from there.



So what of all that is True?



My Bulbs are currently 8 Months Old and I replaced my other Aquariums Lights a Month ago and they are waaaay brighter than my 8 Month Old Bulbs so I think that the 95 Percent intensity at 12 Months is wrong because of that.



What do you guys think?



How often do you guys replace T5 HO Bulbs and why do you pick that time to replace.



Please explain why so all these opinions can be cleared up?