Backlight Bleed Test
Show full-screen black and dark grays to spot backlight bleed and IPS glow on an LCD.
Screen Uniformity Test
Check how evenly your screen is lit by filling it with flat white, 50% gray, black, red, green and blue. Clouding, blotches, darker corners and tint shifts stand out against a single color.
Showing White
Look for areas that seem darker, lighter or a different tint than the center.
Keys: ← → color · F full screen · Esc exit
Runs entirely in your browser. Test results, audio and video never leave your device.
How to check screen uniformity
- Clean the screen, set your usual brightness and dim the room.
- Choose a field with its button and read the tip under the preview: it says what to look for on that field.
- Press Start test, or click or tap the preview, to fill the screen.
- Move through White, Gray 50%, Black, Red, Green and Blue with Next and Previous, the Left and Right arrow keys, Space, Enter or a tap.
- When you see a patch, move your head a little. A patch that stays in place is in the panel; one that shifts with your angle is a viewing-angle effect.
- Press Esc or Exit when you are done.
What is screen uniformity?
Screen uniformity is how evenly a display shows one flat color, with the same brightness and tint in the corners as in the center. Poor uniformity shows as cloudy patches, darker edges, blotches called mura, or faint bands that look like dirt on the glass, known as the dirty screen effect.
How to tell uniformity problems from other faults
Several faults look alike on a flat field. Their shape, where they sit and whether they move with your head tell them apart:
- Irregular patches or bands anywhere on the panel, not only at the edges, that stay put when you move your head: poor uniformity.
- Light coming in from the edges or corners of a dark screen, or a corner glow that changes as you move your head: check it with the Backlight Bleed Test.
- The outline of a taskbar, a logo or a game's status bar that stayed on screen for a long time: image retention or burn-in. Check it with the Screen Burn-In Test.
- Steps or stripes in a smooth gradient: banding, a separate problem that the Gradient Test shows.
Is some unevenness normal?
Yes, to a degree. No panel is perfectly even, and large LCD and OLED TVs in particular often show faint patches or bands on a flat gray. Uniformity also varies between units, so another screen of the same model can look better or worse than yours.
What matters is whether you notice it in real content: a blotch in the sky of a film, bands that stay still while the camera pans across a sports field, or a dim corner behind a document. If you do, note it and contact the seller while the return window is open. Sellers and manufacturers set their own limits.
What this test can detect
- Clouding: lighter, cloud-like patches on gray and black.
- Mura: irregular blotches slightly lighter or darker than the area around them.
- Dirty screen effect: faint bands or smudges on gray that look like dirt on the glass.
- Darker corners and edges, or a center brighter than the rest.
- Pressure marks: small bright or dark spots where the panel has been pressed.
- A tint that changes across the panel, such as one side warmer than the other.
How it works
The page paints the test area with one flat CSS color at a time: White #ffffff, Gray 50% #808080, Black #000000, Red #ff0000, Green #00ff00 and Blue #0000ff. Gray 50% is 8-bit level 128, which a screen that follows the sRGB standard shows at about 22% of the light of white: a mid-tone where blotches and bands stand out.
Start test asks the browser's Fullscreen API to fill the screen, with a fixed overlay where it is not available, and the controls hide after 2.5 seconds without input so nothing covers the panel. Nothing is measured; your eyes make the comparison.
Limitations
- It shows relative differences only. It does not measure luminance or color or give a uniformity percentage; those need a colorimeter or luminance meter read at a grid of points.
- It has one gray level, Gray 50%. Unevenness that shows only in very dark shades needs a darker field, such as Near black 5% in the Monitor Test.
- Viewing angle changes brightness and tint, most at the edges of large or wide screens. Sit centered at your normal distance.
- Some browsers, including Safari on iPhone, keep their toolbar on screen, so the strip under it is not tested.
Frequently asked questions
Which color should I use to check uniformity?
Start with Gray 50%, which shows blotches, bands and the dirty screen effect. Then use Black in a dim room for clouding and other lighter patches, White for darker corners and tint, and Red, Green and Blue for one color shifting in part of the screen, such as red that turns orange.
Why is my monitor cloudy?
Patchy cloudiness on dark scenes is clouding: the LCD backlight does not spread perfectly evenly through the layers in front of it, and pressure from the frame can make it worse. Lowering the brightness makes it less visible. If the whole picture looks hazy or washed out instead, check the black level with the Contrast Test.
Can clouding or the dirty screen effect be fixed?
Not with software: both come from the panel itself. Some monitors have a uniformity compensation setting in their menu that evens out brightness, and lower brightness makes clouding less visible. Do not press on the screen or loosen the frame, which can cause damage. If it bothers you in everyday use, ask the seller or manufacturer about a return or repair.
How do I check uniformity on an OLED screen?
Use a very dark gray as well as Gray 50%. OLED pixels switch off for black, so Black shows nothing, and faint bands and blotches on OLED often show most in dim shades; Near black 5% in the Monitor Test suits that. Gray 50% and White show larger patches and tint.