Annoyingly, the bulbs are non-replaceable, which is pretty irresponsible these days.
Anyway, they say 20,000 hours. Amounts to over 2 years if you leave them on constantly (which you obviously won't.)
In normal use, I reckon that's not bad.
Don't forget, if they admit to 20,000, then they'll probably last even more.
Unless you can find one with replaceable ones, it's most likely the best you can do.