Health & Medicine · Evidence summary

Is dark mode worse for your eyes?

There is no evidence that dark mode damages the eye or makes astigmatism worse, but it is also not an eye-saver for every setting and every person. How comfortable your eyes feel depends on the ambient light, your own refractive state (for example, uncorrected astigmatism), how the screen dims itself, and your viewing habits.

Daytime, well lit

Light mode has the edge. A bright screen constricts the pupil and deepens the depth of field, so text is imaged more sharply. The research points to overall screen luminance, not the color scheme itself, as the key factor.

Night, dim light

Dark mode cuts the total light from the screen. It contrasts less with a dark room, and with a warm color temperature it also interferes less with sleep. Studies disagree on which mode feels less tiring (see "Eye strain" below). Just don't use it in a pitch-black room.

Myopia: early research

One small study is worth noting. In 7 adults, an hour of reading white-on-black text thickened the choroid, while black-on-white thinned it. Whether this slows myopia in children has not been shown.

Which mode should I use? A situation-based recommender

Pick your environment, eyes and device to get a suggestion based on the studies summarized on this page. This is general information, not a substitute for an eye exam.

RECOMMENDATION Light mode

Use light mode (black text on white)

Why, and what to set

    Watch out for

    Based on Buchner et al. (2009), Piepenbrock et al. (2014), Aleman et al. (2018), Xie et al. (2021) and Sengsoon & Intaruk (2025); see the sources below.

    Optics: pupil size, the positive polarity advantage and astigmatic halation

    The brighter the screen, the smaller the pupil. As with stopping down a camera lens, the depth of field grows and aberrations from the edge of the lens are blocked, so the image is sharper. A dark screen emits little light, the pupil widens, and any refractive error that isn't fully corrected becomes easier to notice.

    What is the "positive polarity advantage"?

    Ergonomics research has repeatedly found that reading and proofreading are better with black text on white (positive polarity) than with white on black. Buchner et al. (2009) at the University of Düsseldorf matched the overall luminance of the two displays and the advantage disappeared, so the deciding factor is screen luminance, not the color scheme. Piepenbrock et al. (2014) then measured smaller pupils and better proofreading with black-on-white text.

    Why does white-on-black text look blurry with astigmatism?

    Dark mode does not increase astigmatism, which comes mainly from the shape of the cornea or lens (genetics, frequent eye rubbing, keratoconus). But on a dark background the pupil widens, and the larger the pupil, the larger the blur circle that uncorrected astigmatism casts on the retina, so the edges of white letters seem to bleed, glow or double. This is called halation. In other words, dark mode reveals astigmatism that was already there and not fully corrected.

    Halation demo

    Interactive
    Dark mode (pure white on pure black) DarkMode 123
    Light mode (black on white) DarkMode 123

    * A visual illustration using blur and glow effects, not a simulation derived from experimental data.

    Retina and myopia: ON/OFF pathways and choroidal thickness

    Aleman, Wang and Schaeffel (2018, Scientific Reports) at the University of Tübingen proposed that black-on-white text mainly stimulates the retina's OFF pathway (which detects darkening) and white-on-black text the ON pathway (which detects brightening). They used optical coherence tomography (OCT) to measure choroidal thickness after an hour of reading, with both displays matched at an average luminance of about 35 cd/m².

    1 hour of black on white −16.1 µm

    The choroid thinned, more so in the more myopic subjects. In animal and child studies, choroidal thinning often goes with axial elongation of the eye.

    1 hour of white on black +10.0 µm

    The choroid thickened, regardless of the subject's prescription. Choroidal thickening is generally seen as a signal that inhibits myopia.

    Read with care

    • Only 7 adults (aged 23–29), and the changes were short-term, within one hour.
    • Eye length and refraction were not measured; "slowing myopia" is an inference from earlier research.
    • The authors themselves say a study in children is needed to confirm it.

    Change in choroidal thickness after 1 hour of reading (µm, mean ± SD, N = 7)

    Data: Aleman, Wang & Schaeffel (2018), both eyes pooled.

    Eye strain: instruments and self-reports don't always agree

    Studies of which mode is less tiring are mixed; in Xie et al. (2021) the physiological measures and participants' own ratings even pointed in opposite directions. In Sengsoon & Intaruk (2025), fatigue rose clearly after 1 hour of tablet use in either mode.

    Night-time dark-room study (Xie et al., 2021)

    Simulating night use, the study compared the two modes at six text-background contrast levels. Dark mode produced a higher blink rate and better pupil accommodation, which the authors read as less fatigue; fatigue fell as contrast rose (lowest at 0.969). Yet on the subjective fatigue scale light mode scored lower and was preferred, which the authors suggest may be related to habit.

    One hour of tablet use (Sengsoon & Intaruk, 2025)

    30 women who use tablets heavily (about 11.6 hours a day), crossover design. After an hour, fatigue rose clearly in both modes, with no significant difference between them (p = 0.305); dry-eye scores rose slightly less in dark mode (p = 0.048).

    Designing a dark theme

    Interface guidelines such as Material Design recommend a dark gray surface (for example #121212) rather than pure black, and text that is not glaring pure white. That is design guidance; research has not settled on a "most comfortable" contrast level.

    Scores before and after 1 hour of tablet use (higher means worse)

    Data: Sengsoon & Intaruk (2025), N = 30, means.

    What matters more than the color scheme: flicker, blinking and dark rooms

    When people get sore eyes or headaches after switching to dark mode, the cause is often not the colors but how the screen dims itself or where it is used.

    Low-frequency OLED PWM flicker

    Many OLED screens dim by switching on and off rapidly (PWM); the lower the brightness, the longer the "off" part of each cycle. People sensitive to flicker may get eye pain or headaches from low-frequency PWM in the dark. The IEEE 1789 lighting recommendation treats full on/off flicker as low risk only above 1,250 Hz.

    What to do: turn on high-frequency PWM or a "DC-like / anti-flicker" option, or avoid the very lowest brightness.

    Half the blinks, dry eyes

    According to the American Academy of Ophthalmology (AAO), we normally blink about 15 times a minute, roughly half that when looking at a screen, and often incompletely, so the tear film evaporates. Screen use itself is the main factor; in the studies cited here, dark mode showed a higher blink rate in Xie et al. (2021) and a slightly smaller rise in dry-eye scores in Sengsoon & Intaruk (2025).

    What to do: follow the 20-20-20 rule and deliberately close your eyes fully a few times.

    Phones in the dark and acute glaucoma

    In a pitch-black room the pupil stays dilated for a long time. In people with a shallow anterior chamber and narrow angles (more common in Asians), the dilated iris can block the eye's drainage channel and trigger acute angle-closure glaucoma: severe eye pain, headache, nausea and blurred vision, which need emergency care.

    What to do: keep a bedside lamp on when using your phone at night.

    Blue light and sleep

    The AAO says there is no evidence that blue light from screens damages the retina or causes macular degeneration, and digital eye strain is not caused by blue light. Its clearer effect is suppressing melatonin at night and making it harder to fall asleep.

    What to do: at night, use dark mode with a warm night-shift setting to cut the screen's total light.

    Four practical rules

    No single mode suits every situation; adjusting to your surroundings is the more reasonable approach.

    1. Switch with the environment

    Light mode in daylight and bright rooms; dark mode with a warm color temperature at night or in dim light. Most systems can switch automatically.

    2. Avoid pure white on pure black

    People with astigmatism are especially prone to halation. Use a dark gray background, slightly off-white text, looser line spacing and larger type. The real fix is properly corrected glasses.

    3. Keep a light on at night

    Don't use your phone in a completely dark room; turn on a bedside lamp or night light, and avoid holding the phone close to your face while lying down.

    4. 20-20-20 and full blinks

    Every 20 minutes, look at something 20 feet (about 6 m) away for 20 seconds; place the screen about an arm's length away, slightly below eye level.

    Key studies

    Study Sample and setup Main finding
    Buchner, Mayr & Brandt (2009)
    Ergonomics    		 Polarity and overall screen luminance varied independently The black-on-white advantage comes from higher screen luminance; it disappears when luminance is matched.
    Piepenbrock, Mayr & Buchner (2014)
    Ergonomics 57(11)    		 Pupil size and proofreading measured with positive and negative polarity text Smaller pupils and better proofreading with black on white, consistent with the luminance explanation.
    Aleman, Wang & Schaeffel (2018)
    Scientific Reports    		 7 adults, matched mean luminance, 1 hour of reading, OCT Choroid thinned about 16 µm with black on white and thickened about 10 µm with white on black; effect in children still untested.
    Xie et al. (2021)
    IEEE Access    		 Night-time use, 2 modes × 6 contrast levels Better blink rate and pupil accommodation in dark mode; higher contrast meant less fatigue. Subjectively, light mode felt less tiring and was preferred.
    Sengsoon & Intaruk (2025)
    IJERPH    		 30 female tablet users, crossover, 1 hour per mode Fatigue rose in both modes with no significant difference; small differences in flicker fusion frequency and dry-eye symptoms.

    How this page was made

    This page is adapted from an AI-generated research report, with each study above checked against its original paper or abstract on 2026-10-23. As a result:

    • The report's claim that a dark-mode contrast of 0.725–0.868 is most comfortable and 0.969 should be avoided contradicts the abstract of Xie et al. (2021), which found less fatigue at higher contrast; the page uses the paper's conclusion.
    • "Choudhary et al. (2026)" and a "lexical decision 85.3 ms vs. 119.4 ms" experiment cited by the report could not be found, so they are not included.
    • The sample size of Aleman et al. (2018) (7 people) and the limitations the authors state were missing from the report and have been added.
    • Anything beyond the five studies in the table is general health information and was not checked against the originals, for example: the background on choroid thickness and myopia, the optical explanation of astigmatic halation, the Material Design color example, the "What matters more than the color scheme" section (IEEE 1789, the American Academy of Ophthalmology [AAO], acute glaucoma), the "Four practical rules", and the recommender's notes on sleep, PWM and cataracts.

    This page is general health information and not medical advice. If eye discomfort persists, or you have sudden blurred vision or severe eye pain, see a doctor.