> midpoint of the 0-1 luminance range There are two physical quantities for luminance, relative, and perceptual, so that passed along a nugget for those not as

> midpoint of the 0-1 luminance range There are two physical quantities for luminance, relative, and perceptual, so that passed along a nugget for those not as wise as you who might not know that :) As you know and have mentioned, using 0.5 with the luminance calculation you mentioned, for relative luminance, would be in error (I hate being pedantic, but it's important for some parties, a11y is a de facto legal requirement for a lot of work, and 0.5 would be spot on for ensuring WCAG 2 text contrast as long as used with perceptual luminance, L*) > doesn't align with human perception It is 100% aligned with how humans perceive brightness, in fact, it's a stable work product dating back to the early 1900s. > Ultimately one could use 0.18-0.3 as threshold Perceptual luminance and relative luminance have precise mathematical definitions, one can be calculated in terms of the other. If you need to hit contrast K with background color C, you won't be able to treat this as variable. What you pass along about it being variable is valuable, of course, in that, given K and C, output has a range, i.e. if contrast algo says you need +40 L* for your text to hit APCA/WCAG whatever, and your C has 50 L*, your palette is everything from 90 L* to 100 L* and 0 L* to 10 L*.