How long does the average UV bulb last?

If it runs constantly, then yeah, you should change it every year.

I think they are designed for around 8000 hours of use certainly the one in my vectron v2 600 said change every 8000 hours, mine has a series of lights as a timer green upto 4000 hours, orange between 4000-8000 hours and then red after 8000 hours.It is then changed and the light timer resets.

I would say that 1 year on 24/24 hrs basis is too much...I go ( with some leeway admitted ) for 6 month intervals..

well a UV must be turned on 24/7 as far as i know parasites don't sleep

average UV bulbs last 6 months their are some on the market that last 1 yr

I used to run two 57-watt UV's when I had my pond. I replaced the bulbs every 6-8 months, the bulb really starts losing its effectiveness after 6 months of 24hr usage.

Old bulbs always glowed a light blue/purple color, the new bulbs always looked more white when glowing, (dont look directly at the bulbs will kill your eyes)