Screen Uniformity Test
Fill your screen with even grey and colour fields to spot darker corners, dirty screen effect (DSE) on grey, clouding on near-black, and tint shifts. Mark each part of the panel on the 3×3 grid. Free, runs in your browser.
Uniformity checker
Dim the room, set the monitor to its normal brightness and sit at your usual distance, square to the centre. Start the test and look at the whole panel at once rather than one spot. Click, tap, swipe or use the arrow keys to change field. G toggles the 3×3 zone grid. The X button stays on screen, and Esc exits too.
Grey names are 8-bit code values, the colour painted on the screen. 50% grey is #808080. That is not a perceptual mid grey, and this page does not measure nits.
Jump to a field
Keys: → ↓ Space Enter next, ← ↑ back, G toggles the zone grid, Esc or the X button exits. The X button stays visible. Enter and Space do not change field while Previous, the grid button or Exit is focused. On phones that block the Fullscreen API (iPhone Safari), the test fills the browser window instead.
Mark each zone
Run the grey fields with the zone grid on, then mark each numbered zone below. Compare zones with each other, not with a perfect ideal: every panel is a little brighter in the centre. Your marks are saved in this browser.
Mark a zone after you look at it. These notes are not a uniformity percentage.
Reading a uniformity test
What non-uniformity looks like
Vignetting is the most common issue: corners and edges darker than the centre, easiest to see on 50% grey and white. Dirty screen effect (DSE) shows on grey fields, often from 20% to 50%, as blotches or faint vertical bands. The marks can follow the shape of a picture that used to sit on the panel. They are easy to miss on a still image and stand out when the picture moves, such as a football pitch or a sky in a game. The panning 30% grey field is for that. Clouding is not DSE. It is bright, soft patches on dark fields, from uneven pressure on an LCD backlight, which is what the 5% and 10% greys are for. Tint shifts show up as a pinkish or greenish zone on grey. IPS glow is separate: it changes when you move your head, while real unevenness stays put. Check glow and edge bleed on black with the screen bleeding test.
The panel lottery
Uniformity depends on how evenly the backlight, diffuser and panel layers were assembled, so two units of the same model can look very different. A "premium" badge or a factory calibration report does not guarantee an even panel; that report usually measures the centre only. If you see a zone that is clearly darker or tinted on 20% to 50% grey and it also shows in normal use, an exchange inside the return window is reasonable. Chasing a perfect panel across five swaps usually is not.
OLED near-black
OLEDs have no backlight, so they avoid clouding but often struggle at 5% and 10% grey: faint banding, blotches or a slight tint as pixels barely switch on. Mild near-black unevenness is normal on OLED and tends to be invisible in real content. Pair this test with the black level test to see where your screen starts crushing shadows.
Photographing it honestly
Phone cameras exaggerate uniformity problems. Long exposure, auto brightness and lens vignetting make any panel look patchy. Judge with your eyes first. If you need a photo for a return, shoot straight on from a few metres back with exposure locked so the grey looks as it does in person, and say so.
Related tools
- Screen Bleeding Test: find backlight bleed and IPS glow at the edges.
- Dead Pixel Test: spot dead, stuck and hot pixels on solid colours.
- Black Level Test: check shadow detail and near-black steps.
- Display Test: a full set of monitor test patterns in one place.
Frequently asked questions
What is dirty screen effect (DSE)?
Dirty screen effect is blotches or faint bands on a grey field. The marks often follow the shape of a picture the panel has shown, and they stand out when that picture moves, such as grass or sky. Look on the 20% to 50% greys. The panning field is 30% grey (#4d4d4d) with a soft bar crossing it. Blotches that stay put while the bar moves are DSE. If reduced motion is on, the bar stays off.
What is clouding, and how is it different from DSE?
Clouding is bright, soft patches on a dark screen, from uneven pressure on an LCD backlight. Look for it on the 5% and 10% greys in a dim room. DSE is the blotchy or banded look on the 20% to 50% greys and does not need a dark room. Edge glow and backlight bleed show on black. This page has no pure black field. Use the screen bleeding test for that.
Why use grey instead of only black?
Black hides DSE and vignetting. Grey shows darker corners, tinted zones and dirty patches. Near-black grey (5% and 10%) is where clouding shows. The 20% to 50% greys are where DSE shows. White shows darker edges. Red, green and blue show a zone whose hue has shifted.
How do I leave the full-screen test?
Use the X button along the bottom. It stays visible on white, grey and black, including on a phone. On a keyboard, press Esc. Closing the test also leaves full screen when the browser entered it. Arrow keys, a click or a swipe change the field. Enter and Space do that too, unless Previous, the grid button or Exit is focused. Those buttons then do what their labels say.
Does this page measure nits or a uniformity percentage?
No. It paints solid fields for you to look at. It cannot read brightness in nits, and the zone buttons are not a uniformity score. OK, Darker and Tinted are notes you make by eye. Compare one zone with the others on the same field.
What do the grey percentages mean?
They are 8-bit code values, the same CSS colour on the screen. 5% is #0d0d0d, 10% is #1a1a1a, 20% is #333333, 30% is #4d4d4d, 50% is #808080 and 75% is #bfbfbf. 50% grey is about half of 255 on each channel. It is not a perceptual mid grey and not half the screen brightness.
Why does the test not cover the whole phone screen?
Some phones, including iPhone Safari, block the Fullscreen API. The test then fills the browser window instead. Turn the phone sideways, or scroll so the address bar tucks away, then start again. There is often no Esc key, so use the X button to leave.