Display Permanence Rating.

A WIR Display Permanence Rating is a number of years, published by Wilhelm Imaging Research for one specific ink and media combination, before fading or a shift in color balance becomes noticeable. It is not one number but three, because the rating is published per display condition: prints framed under glass, prints framed behind a UV filter, and prints displayed unframed under bare-bulb illumination, with a separate album and dark-storage rating alongside them. The years come from accelerated light-fading tests extrapolated to an assumed display condition of 450 lux for 12 hours a day, which is an assumption about someone's wall rather than a measurement of it. ISO test methods for print permanence exist, and WIR sits on the ISO group writing them, but the same reports are blunt that no ISO or ANSI specification standard exists for turning a test result into a lifetime or noticeable-change prediction under a standardized set of display and storage conditions. They show what that gap costs: Kodak's assumption of 120 lux alone made its display-life predictions 3.75 times greater than those from WIR and other manufacturers. So a shop quoting bare years to a wall-art customer is quoting an assumption. Quote the display condition with the number, or wait for the complaint from the person who hung the print in a window.