Most Night Sights will last 8-10 years. I've got some that are several years old that are just as bright as new.
The color you choose is a big factor...
My experience with colored (non-green) PT sights indicates they'll last a year (or less, in my case)and then slowly dim to uselessness. Several friends have had similar problems with the colored PT sights.
I recently sent some red/orange PTs that were 9 months old back to PT for warranty replacement. They did the replacement for $7 -- to cover shipping -- with no complaints.
Their rep said that their (and most other) red or orange sights are less bright than green. He said he generally tries to talk folks out of using the red or orange sights when they are first ordered.
I had them replace the orange front and red rear with green. I'm glad I did.
[This message has been edited by Walt Sherrill (edited March 26, 2000).]