Dark mode is not a style choice.

Design · 5 min read

Two separate clients asked for dark mode in their apps. Both assumed it was a simple toggle. Flip a switch, invert the colours, done. One was building an education app for adult learners. The other was building a vehicle management tool. Both wanted dark mode because it looked modern, sleek, and professional. And both were surprised when I said we needed to talk about it before committing.

Dark mode isn't a style decision. It's a usability decision. And for certain audiences, defaulting to dark mode can make the app genuinely harder to use.

What happens to your eyes after 40

Contrast sensitivity starts to decline around age 40. The lens of the eye gradually yellows, the pupil gets smaller, and the ability to distinguish fine detail against a dark background drops. White text on a dark background, which looks crisp and clean to a 25-year-old, can start to blur and halo for someone in their mid-40s or older. Especially at smaller text sizes. Especially on a phone screen.

Research from Nielsen Norman Group, published by Raluca Budiu in 2020, found that light mode is generally better for readability across users. And the difference increases with age. For younger users with good vision, dark mode and light mode perform roughly the same. But for older users, light mode is measurably easier to read.

That matters a lot when your audience skews older. The education app was targeting adult learners, many of them over 40, studying for professional qualifications. These people are already working harder to absorb new information. Making the text harder to read on top of that isn't a design choice. It's a barrier.

The default matters more than the option

You can absolutely offer both modes. That's fine. The question is which one you default to, and why. Most users never change defaults. They use whatever the app gives them out of the box. So if your default is dark mode and 40% of your users are over 40, you've just made the default experience worse for a huge portion of your audience.

For the education app, the answer was clear. Default to light mode. The primary use case is reading and studying. The content is text-heavy. The audience includes a significant number of people over 40. Light mode by default, with dark mode as an option for those who prefer it. The decision wasn't about what looks better. It was about what works better for the people who'll actually use the app.

For the vehicle management app, it was a different conversation. Mixed-age users. Shorter reading tasks. More dashboard-style interaction. The trade-offs were different, but the principle was the same: choose the default based on your users, not your taste.

Design for eyes, not for screenshots

Dark mode photographs beautifully. It looks incredible in App Store screenshots, on landing pages, and in pitch decks. That's part of why clients ask for it. They've seen other apps use it, and it looks premium. But the App Store screenshot isn't the experience. The experience is a 45-year-old electrician trying to read a study question on his phone at 10pm after a full day of work.

Dark mode isn't bad. I want to be clear about that. For some apps and some audiences, it's the right call. Coding tools, media players, apps used primarily at night. All good candidates. But the decision should be driven by who your users are, how they use the app, and what the research says about readability for that audience. Not by what looks best in a mockup.

The next time someone says "let's do dark mode," ask one question first: how old are the people using this? The answer might change the whole conversation.

Sources
Dark Mode vs. Light Mode (Budiu, 2020, Nielsen Norman Group) - Light mode is generally better for readability, and contrast sensitivity declines significantly after age 40.

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