so if i use photochromic lens regularly instead of my iridium lenses it will wear off after significant amount of use.Yes, but maybe more salient is that their function is also severely compromised after a certain amount of use- from what I've read this is more likely to happen before the yellowing. The lenses have a finite number of times they can darken and lighten. How many? I've read conflicting accounts but I know several people who wear them in eyeglass applications that say after 2-3 years they're shot. Now granted that's when they're being worn 18 hours a day 365 days a year - a sunglass won't get that much use presumably. All that said should that discourage purchase of a photochromic lens? No. But it's a consideration along with other aspects such as the fact they make lousy automobile driving lenses because most auto windows filter a certain amount of UV and UV is what photochromics react to so in cars they don't darken enough.