The half-life of tritium is 12.33 years. Yes, I'm a radiation physicist. That being said, the job plus a $1.50 will get you a cup of coffee.
Anyway, that means the amount (intensity) of light that you see will be cut in half every 12.33 years. That also means that after two half-lives (24.66 yrs), the light intensity would be reduced to 1/4 of its intensity "right now."
Now, the practical aspects of all this stuff. I don't like bright sights. If you have "fresh" tritium sights, just think if that perp in the night comes around behind you. Heck, he can see you from 15 feet away; or at least he can see the gun's sights, both front and rear.
I have purposely installed a front sight on some of my guns that other folks "threw away" when they got new ones. Of course, the gunsmith keeps them in his drawer and will give them to you free. The used front sight is plenty bright enough to see in a darkened situation without being any brighter than necessary.
And, you saw that I said front sight only. That's the only sight you need to see, especially at rather close range. At 25 yds, the front sight alone wouldn't be enough, but you can't see the perp that far away anyway.

And to RBurg who doesn't like Glocks...I'm sorry you got a bad one. Never heard of a bad Glock. I have/had eight of them, my son-in-law SWAT cop has several and I've shot them for twenty years without a misfire. I would never be able to say that about some Smith semi's I have known.
Sonny