PC Lighting - Lifespan?

[Levek]

hey all,

(first post here)

I am a new salt-water-er, reef-er, etc...
I have a 10g nano tank doing quite well so far. It is about 6 months old now. I am wondering, in general, what sort of life span I should be expecting from my light fixture? I have a Coralife 20" AquaLight Fixture - 96W - PC. How often to people usually change their bulbs?

Thanks for the advise.

Levek