Why ‘dark mode’ causes more accessibility issues than it solves
Dark mode. Isn’t it marvellous? All cool and trendy and accessible and sustainable. It even helps offset the damage you’re doing to your circadian rhythms by checking your phone before you turn out the lights.
Winning.
So it’s great that every app is introducing a dark mode setting.
Or is it?
Turns out, for some people it’s not accessible at all.
What’s the problem?
Dark mode causes something called “halation” which massively impacts how people with astigmatism perceive digital interfaces.
I learned about halation effect some time ago, when I was asked to review the usability (and therefore the accessibility) of an interface using yellow on black and white on black because it was more “accessible”.
As it turned out, it was more accessible for this client’s users (who were partially sighted) but not for me, because I have astigmatism.
So like a good UXer I went off to find out why.
What is astigmatism?
Astigmatism is a condition affecting a large percentage of humans. You find different stats everywhere, but in the UK it’s roughly 47% who need corrective treatment for this condition (by which we mean glasses or contact lenses in order to be able to see properly).
Here’s a definition from the NHS website:
Astigmatism means your eye is shaped more like a rugby ball than a football, so light is focused at more than one place in the eye.
This can cause:
• blurred vision
• headaches
• eye strain (you may notice this after concentrating for a long time — on a computer, for example)
Astigmatism normally occurs alongside short sight or long sight.
Source: NHS
Actually it turns out that most peoples’ eyes aren’t perfect, and most people have some level of…