Had to dig to find it, but I bought it new in 2011 from Midwayusa and the Rings are Nightforce medium. Looks like Half life of tritium is 12.5years, so half as bright by the year 2024, and down to about 25% after 22 years, or year 2033.
Looking through it its still seems as bright as it was when new, but without a side by side with a new one that is pretty subjective.