In message , JR
writes
I fitted a flourescent light fitting just over a year ago in the
kitchen, which worked fine, but has recently begun to start off fairly
dim, before brightening up over the course of a few minutes, although
to nowhere near as bright as it used to be.

It's got a circular 60w tube (360w equivalent apparently - it was very
bright when I fitted it) which costs about 12GBP to replace. Before I
get a new one, can anyone tell me whether these symptoms sound like
it's the tube or the electronic ballast that's dying?

Sounds like the mercury vapour has been depleted, perhaps by being
absorbed into the phosphor or into the amalgam that may have been used
to dose the tube in the first place. Does the tube light up a dull pink
when initially turned on? If it does then it's probably the lamp.

The slow brightening is down to the mercury vapour gradually releasing
back into the lamp as it warms up.

--
Clive Mitchell
http://www.bigclive.com