Pure black grounds with pure white type contrast too hard
Aliases: halation · blooming · OLED black · excessive contrast
What it is
An OLED background at #000000 with body type at #FFFFFF makes letters feel as if they glow and strokes fatten, especially for people with astigmatism. More contrast is not always better. A dark reading surface wants near-black grounds and near-white type, so the stimulus is “ink and paper under dimmer light”, not “a lamp in a void”.
This is about halo and fatigue from too much contrast, not about the threshold for being able to read.
Why it happens
Light strokes bleed into a dark field — irradiation: scatter on the retina plus optical aberrations make white letters look wider than their geometry. Astigmatism, uncorrected refractive error and a dirty screen enlarge the bleed. True black on OLED drives surround luminance near zero and pushes simultaneous contrast to the end of the display chain, so bleed is worst; LCD leak actually lifts the floor and eases it.
Adaptation adds another layer. Pupils dilate over a large true-black field, so type behaves more like point sources. Raising the background to dark grey and dropping type to light grey lowers the ratio, and halo and glare fall together. This can be true at the same time as “too little contrast cannot be read”: too low fails recognition, too extreme is readable but unpleasant.
Studying it
Use a reading task plus a discomfort scale. Independent variables: background L* (0 / low / mid), type L*, panel type (OLED / LCD), self-reported astigmatism. Dependent variables: reading speed, error rate, ratings of dazzle or “letters are glowing”, apparent stroke width (a matching task: observers adjust a line to the felt weight).
Do not assume “higher contrast, better score”. Expect a U: both extremes are worse, a middle band is fast and less tiring.
Where it stops holding
- High-contrast mode’s users may need that extreme split; do not force reading-theme near-black/near-white on them.
- Large titles and short labels tolerate pure black and white better; the problem concentrates in paragraph reading.
- In bright ambient light, white on true black may not halo — screen glare becomes the first problem.
- Showing that a pairing is “too extreme” does not require quoting an accessibility ratio; a pair can meet a ratio and still bloom.
Applying it
- For dark reading surfaces use a dark-grey ground you can tell from true black, with light-grey body type. Do not press lightbox white onto void black.
- Reserve true black for large media beds that need power saving or a cinematic frame, not as a body-text ground.
- Inside one dark theme, card surfaces should sit a little lighter than the window, which also eases the extreme gap between type and ground.
- How to check: read two screens of long copy on the target OLED and ask whether letters glow or strokes feel heavier than in the light theme. If yes, lift the background and drop the type until the glow goes and reading stays easy.