White text on a black background is the highest-contrast pairing a screen can produce — a 21:1 ratio, the maximum WCAG can measure. So why do so many readers find it tiring? The answer is that readability is not just contrast; it is how our eyes handle light.
What happens to your eyes on a black background
On a dark screen, pupils dilate to let in more light. A dilated pupil focuses less precisely, so bright letterforms scatter slightly on the retina — an effect called halation, where white strokes appear to glow and bleed into the black around them. For most people this is a subtle fuzziness; for people with astigmatism (roughly a third of the population) it can be genuinely uncomfortable, sometimes even producing a double-vision-like effect.
When white-on-black works well
Dark interfaces earn their popularity in specific conditions: low ambient light (night reading, dim rooms), OLED screens (true black pixels switch off, saving battery), short-form content (menus, dashboards, code editors where text comes in fragments), and for users with light sensitivity or certain low-vision conditions who genuinely read better on dark. That is why dark mode should always be a choice, never the only option.
When it hurts
Long-form reading in normal lighting is where pure white-on-black performs worst. Sustained halation fatigues the eyes faster than dark-on-light, and reading speed measurably drops for most users. Print has used black text on white for centuries for a reason.
How to do dark mode right
- Soften the whiteUse off-white text (#E8E8E8 to #F2F2F2) instead of pure #FFFFFF — it cuts halation with almost no contrast loss.
- Soften the blackVery dark grey (#0F1115 to #16181D) reads as black but reduces the pupil swing. See our black background shades.
- Lighten font weight slightlyLight strokes bloom on dark; a slightly lighter weight compensates for perceived thickening.
- Verify the ratioAim for at least 4.5:1 for body text (WCAG AA) — softened pairs still pass easily.
Test any color pair yourself with our free contrast checker — live WCAG ratios as you pick.
Frequently asked questions
Is white on black better for your eyes?
In dark environments, usually yes. In bright environments and for long reading, dark-on-light generally causes less fatigue. The honest answer is: it depends on lighting, duration and your eyes.
What contrast ratio is white on black?
Pure #FFFFFF on #000000 is exactly 21:1 — the maximum possible. Softened pairs like #E8E8E8 on #16181D still score around 14:1, far above the 4.5:1 requirement.