Real world accuracy of WCAG contrast formula?

[incyphe]

Hello,

I'm a UX practitioner and it's my first time posting :)

In general, I find that WCAG's calculated ratios do good job of indicating perceived contrast. Looking under the hood, I see that it uses sRGB transformation formulas to accounts for non-linear ways in which people eyes perceive light, varying perceived luminescence of different colors, as well as ambient light factor. All amazing stuff.

However, I can't help but notice one missing thing, which is, consideration for the fact that most people run their displays far brighter than sRGB recommended viewing spec of 80 cd/m2.

Most people have their displays at 250-300. White point on 300 cd/m2 will look far brighter than the one calibrated to 80-100 cd/m2.

Possible consequence is, the formula underestimates real-life contrast of light on dark elements. In below screenshot, you'll see that 3:1 in the last column is far more legible than 3:1 or even 3.2:1 on other columns.

I notice that the effect goes down with dimmer LCD setting, but still present.

I know there are few other factors at play too including contrast setting, font choice, etc, but this is something I've observed over a few years across multiple devices.

What do you think?

Typeface replaced with rectangle blocks.

[JAWS-test]

Related: #360 and #695

[incyphe]

Thank you. It has overlap with #695

I will close it.