If you mean the tritium, the half-life is 12.5 years. But as mentioned above, any time there’s skylight, the fiber optics carry the load. For better control of the illumination, get a battery-powered model. All of them are usable sans illumination, just select a reticle that is good for you both ways. The duplex in the 3-9 Accupoint is excellent, lit or not. The website has really detailed reticle illustrations for each model to help you pick. It’s important to check the specific model when you look because the dimensions vary a lot, even for the same reticle type.
