If white text on a black background looks doubled, ghosted or like it is glowing at the edges, you are not imagining it — and you are far from alone. The effect has a specific optical cause, and a few settings changes usually eliminate it.
The cause: astigmatism meets halation
In a dark environment your pupils open wide. A wide pupil exposes more of the eye’s lens — and if that lens has even mild astigmatism (an irregular curvature that affects roughly one in three people, often uncorrected), incoming light focuses at slightly different points. Bright shapes on dark backgrounds are exactly the worst case: the glowing letterforms smear directionally, producing a ghost copy above, below or beside each stroke. On light backgrounds the pupil constricts, the lens irregularity matters less, and the doubling disappears — which is why the same person reads paper perfectly.
Five fixes that work
- Switch long reading to light modeThe constricted pupil masks mild astigmatism almost entirely.
- If you keep dark mode, avoid pure white textOff-white (#E0E0E0 range) on dark grey dramatically reduces the glow that creates ghosts.
- Increase font size and weight slightlyThicker strokes survive smearing better than thin ones.
- Raise ambient lightA lit room constricts pupils even with a dark screen.
- Get your eyes checkedIf ghosting appears in daily life too, an optometrist visit is worth it — mild astigmatism is very correctable.
Related reading: the full readability breakdown of white-on-black, and designing white text on dark backgrounds properly.
Test any color pair yourself with our free contrast checker — live WCAG ratios as you pick.