I bought a Micro CDP today with tritium sights. I also have a 10 year old Stainless TLE II with tritium sights. Here they are side by side. The front sights are close to each other.
Here are the new sights
And the old
Now, these were taken with a cell phone camera. It had a hard time focusing. So, the images are a little worse than real life. However, you can see a real difference after 10 years. The half life of tritium is 12.3 years, which means in that amount of time, the sights should be half as bright. I've been thinking for a couple of years now that I need to replace these sights.
Both guns were NIB when I bought them. These TLE II sights have degraded more than I expected. I can see them, but it is hard to pick out the front sight. Having said that, I just checked and replacement sights are only $129. Meprolight covers these for 12 years.
Are these still usable? Yes, they are.
Are they satisfactory? Not anymore. They look they have lost more than half of their brightness.
Do I care? Not really, I got good use from them. I'd rather have bright sights than split hairs over what is useable.
I was curious when I bought this gun as to how long they would last. I think what I'll do now is put my sights on a 8 year replacement cycle. That's when I first started to really notice they were getting dim. As I've said, they are still useable, but they are no longer satisfactory. I'll keep the old sights and watch them as they fade over the years. It will be interesting to see what they look like in 2 more years, which will be the warranty expiration.