The good, the bad and the unreadable

This morning, I stood in the sun at the bus stop and tried to quickly check something on the City of Gothenburg website. But it didn’t go well, not because the sun was glaring on the screen, but because the font was so thin that it practically disappeared.

The colour contrast meets the legal and standard requirements, but for me, standing in bright sunshine, a bit over 45 years old and with a mild dyslexia, the text became a gray blur. It was simply too hard to read. Not because the contrast was too low – but because the letters were too thin.

It’s a reminder of something that is easily forgotten, even in carefully designed interfaces – a thin font can kill legibility. Not just for those of us who check our phones outdoors, but also for aging eyes, tired eyes, people with dyslexia or anyone with low vision.

EN 301 549 and WCAG 2.1 and 2.2, require sufficient contrast (9.1.4.3 Contrast (minimum)). The requirement is that text should have sufficient contrast against the background, at least 4.5:1 for plain text. But there is no mention of the thickness of the letters. That’s why a super-thin greyish font might technically pass – but still fail in practice.

The thinner the typeface, the more it relies on perfect contrast and ideal lighting. Research supports this too, thinner text is slower to read and more mentally taxing, especially on small screens and for older users. In a 2001 study, Bernard, Liao, and Mills showed that both reading speed and comprehension declined when the text was too thin or too small – not just for older readers, but across the board.

In addition, for people with dyslexia, it is common for letters to merge or change places. It doesn’t help if the text looks stylish, if it’s too hard to grasp.

Design choices such as thin fonts might feel modern and clean, but not if they sacrifice legibility. Great design happens when you understand the basics, like contrast, readability and clarity, and work creatively within those constraints. That’s when form and function really come together. It’s not the thin font that makes a design great; it’s the ability to create something that works well and looks good for as many as possible.

So next time you’re picking a font for the web, don’t just focus on how it looks in a design mockup on a retina display in a cozy office indoor. Following the standards and ticking off requirements isn’t enough. We need to look around and see the real world. How do users experience the text? Think about how it feels to stand in the sun with tired eyes, reading glasses or a brain that sometimes flips letters around.