On Mar 12, 5:04 pm, KLS wrote:
... has been running continuously for
a good 4 years now with no sign of fading.

This is probably a technical impossibility given how flourescent bulbs
work. I am sure if you comapred it to a new bulb of similar output
there would be a noticable difference. I replaced one of two ~3 YO
bulbs in a fixture the other day and the new one is quite a bit
brighter. Oh, they came from the same pack.