Dark mode isn’t the universal eye-saver it’s marketed as. While it can help in specific situations, like using your phone in a dark bedroom, it introduces real drawbacks that most people don’t expect: blurrier text, harder focusing, and in many cases, more eye strain rather than less. The problems stem from how your eyes physically respond to light-on-dark displays.
Your Pupils Work Against You
When you switch to dark mode, your screen emits less light overall. Your pupils dilate to compensate, just as they would in a dim room. A dilated pupil lets in more light, but it also reduces your depth of focus. Think of it like a camera lens: a wide aperture produces a shallower depth of field, meaning less of the image is sharp at once. A constricted pupil, like a narrow aperture, keeps more of what you see in crisp focus.
This is why text on a bright white background often looks sharper. Your pupils tighten, and the image landing on your retina has cleaner edges. In dark mode, dilated pupils can make fine details on screen slightly fuzzier, forcing your eye muscles to work harder to maintain focus. Over a long reading session, that extra effort adds up.
The Halation Problem With Astigmatism
Roughly one in three people has some degree of astigmatism, a condition where the eye’s cornea or lens isn’t perfectly round. For these people, dark mode can be genuinely worse. White text on a dark background causes an optical effect called halation, where bright letters appear to bleed or smudge into the surrounding darkness. The edges of characters lose their crispness, and words can look like they’re glowing or spreading outward.
This forces your eyes to work harder to define where each letter begins and ends. If you’ve ever noticed that dark mode makes text look fuzzy or tiring to read, and you can’t quite explain why, uncorrected astigmatism is a likely culprit. The effect gets worse with smaller font sizes, which is exactly how most people read on their phones.
Reading Performance Is a Mixed Bag
The research on reading speed and dark mode doesn’t tell a simple story. One study of young adults found that participants actually read slightly faster in dark mode (about 136 words per minute versus 128 in light mode), with no meaningful difference in reading errors like mispronunciations or skipped words. That might sound like a point in dark mode’s favor, but speed alone doesn’t capture the full picture.
The visual fatigue that builds over time, the extra focusing effort from dilated pupils, and the halation effects for people with astigmatism all compound during longer reading sessions. A quick glance at a notification in dark mode is very different from reading a long article or working in a document for hours. Short-term speed tests don’t measure the strain that accumulates over a full workday.
Bright Rooms Make It Worse
Context matters enormously. The ideal setup is to minimize the contrast between your screen and the environment around it. In a well-lit office or a room with daylight coming through the windows, a dark screen creates a harsh mismatch. Your eyes constantly adjust between the bright surroundings and the dim display, which is a recipe for fatigue.
Dark mode makes the most sense in a dimly lit room, where a bright white screen would be the thing creating that same uncomfortable contrast. In darkness, a glowing white page is essentially a flashlight pointed at your face, and switching to dark mode brings the screen closer to the ambient light level. But if you’re using dark mode during the day in a bright environment, you’re likely creating the exact problem you thought you were solving.
It’s Not Great for Dyslexia Either
People with dyslexia tend to read better with lower contrast color combinations, not the stark white-on-black that dark mode typically provides. Research from the W3C Web Accessibility Initiative found that while readers without dyslexia overwhelmingly preferred black text on a white background (about 33% chose it as their favorite), only around 14% of participants with dyslexia made the same choice. The fastest reading speeds for dyslexic readers came from black text on a cream background, not from either extreme of pure light mode or pure dark mode.
Interestingly, people’s personal preferences didn’t always match what actually helped them read better. The color combinations readers said they liked weren’t necessarily the ones that produced faster, more accurate reading. This suggests that if you have dyslexia and find dark mode comfortable, it may still be worth experimenting with softer, lower-contrast color schemes to see if your actual reading improves.
What Dark Mode Actually Does Well
Dark mode has legitimate benefits, just not the ones most people assume. The American Academy of Ophthalmology recommends setting devices to dark or night mode in the evening because the warmer, dimmer display is less likely to interfere with your body’s sleep signals. It’s not about protecting your eyes from damage. It’s about not tricking your brain into thinking it’s daytime when you’re trying to wind down.
Battery life is the other genuine advantage, at least on phones and tablets with OLED screens, where dark pixels use less power. And for people who work in dark environments (video editors, astronomers, anyone using a screen in bed at night), dark mode reduces the blinding effect of a bright display in a dark room.
When to Skip Dark Mode
If you do a lot of reading or text-heavy work, light mode is generally the better choice during daytime hours. This is especially true if you have astigmatism, work in a well-lit space, or find yourself squinting at text in dark mode. The pupil dilation and halation effects are real, and they disproportionately affect people doing sustained reading.
The most practical approach is to treat dark mode as a tool for specific conditions rather than a permanent setting. Use it at night, in dark rooms, or when you’re mostly looking at images and video rather than reading dense text. During the day, in a bright environment, with paragraphs of text in front of you, light mode is doing your eyes a favor, even if it doesn’t feel as sleek.