Screen Uniformity Test
Check how evenly your monitor lights up from corner to corner. This test fills the whole screen with solid grey, white, and pure red, green, and blue fields so you can spot clouding, backlight unevenness, mura, and tint shifts by eye. Run it full-screen in a dark room and compare each corner against the centre — an optional 3×3 grid helps line the regions up.
← → ← → change field · G grid · Esc exit
Photographing the screen exaggerates unevenness. Judge by eye at a normal distance in a dark room, after a few minutes of warm-up.
Soft, uneven patches of brighter light, most visible on low-to-mid greys. Called the dirty-screen effect when it looks like faint smears.
A silvery or warm sheen in the corners of IPS panels that brightens and fades as you shift your viewing angle.
Edges and corners looking dimmer than the centre — partly real falloff, partly the steeper viewing angle at the panel edges.
Fine-grained blotchiness or graininess baked into the panel at the factory, fixed no matter your viewing angle.
- 5% grey — Deep shadow — near-black clouding and the dirty-screen effect
- 25% grey — Low-mid tone — clouding and dirty-screen effect show most here
- 50% grey — Mid grey — overall brightness evenness and mura
- 75% grey — Light grey — vignetting and dimmer edges and corners
- White — Peak white — tint shifts, warm or cool corners, and smudges
- Red — Red channel uniformity and blotchy tint
- Green — Green channel uniformity and faint banding
- Blue — Blue channel uniformity and corner tint
What panel uniformity is
Uniformity is how consistent a display's brightness and colour are across the whole panel when it shows a single flat tone. A perfectly uniform screen would render a 50% grey as the exact same grey in every corner and at the centre; in practice, LCDs vary because the backlight, diffuser layers, and liquid-crystal cells are never perfectly even. Small differences are normal and usually invisible in real content — this test deliberately uses flat full-field patterns, which are the worst case, so any unevenness stands out. Judge it the way you actually use the screen: by eye, at a normal distance, not with your nose against the glass.
What causes non-uniformity
- Backlight and diffuser: edge-lit LCDs push light in from the sides, so brightness can fall off or pool unevenly across the panel, while local-dimming and diffuser imperfections add their own variation.
- Panel lottery: units of the same model vary from the factory. Two identical monitors can have noticeably different clouding or tint because of normal manufacturing tolerances.
- Mura: fine, fixed blotchiness or graininess baked into the panel during production. It does not move when you change your viewing angle.
- Pressure and handling: over-tight bezels, shipping stress, or pressing on the screen can create bright or dark patches, some of which relax over time and some of which are permanent.
- Temperature and warm-up: brightness and tint can drift for the first several minutes after power-on, so let the display settle before judging it.
Clouding vs bleed vs glow
These three are easy to confuse. Clouding (also called the dirty-screen effect when it looks like faint smears) is soft, uneven patches of brighter light spread across the panel, most visible on dark-to-mid greys. Backlight bleed is bright light leaking from the very edges and corners on a black screen, and it stays put when you move your head. IPS glow is a silvery or warm sheen in the corners that noticeably brightens and fades as you change your viewing angle — that head-movement test is the reliable way to tell glow (angle-dependent) from bleed (fixed). This tool focuses on clouding and overall evenness on lit greys; the Screen Bleeding Test is the better fit for edge bleed and glow on pure black.
Why edges and corners look dimmer
Some edge dimming is real light falloff from an edge-lit backlight, but a lot of it is geometry: at the edges of the panel you are viewing the pixels at a steeper angle than at the centre, and every LCD loses a little brightness and shifts colour off-axis. That is why corners can look dimmer or tinted even on a genuinely uniform panel, and why the effect changes as you move or sit more square to the screen. VA panels tend to shift contrast more with angle, IPS panels tend to glow, and both show some vignetting on a full white or light-grey field. Move your head to separate true, fixed unevenness from angle-dependent effects.
Related tests
- Screen Bleeding Test reveals edge backlight bleed and IPS glow on a pure-black screen.
- Dead Pixel Test finds stuck and dead sub-pixels with solid full-screen colours.