Screen uniformity test
Flat grey fields at any level you choose, with an optional zone grid for describing exactly where a problem sits.
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A grey level is a code value, not a share of emitted light. 50 per cent here means code value 128, which emits roughly 21 per cent of maximum luminance because of the sRGB transfer curve. That is why mid grey looks darker than you might expect.
How to run this test
- Go full screen at 50 per cent and step back to the distance you normally sit at. Uniformity is a whole-panel property and is misleading from close up.
- Look for bands, blotches and regions that sit at a different brightness or a different tint from the rest.
- Drop to 5 or 10 per cent. This is where clouding and backlight problems live on an LCD.
- Go up to 75 or 100 per cent for highlight uniformity and edge dimming.
- Turn on the zone grid if you need to describe where a problem is, for a support ticket or a forum post. Turn it off again before judging anything.
What a problem looks like
- Vertical or horizontal banding
- Regular stripes running the full height or width of the panel, usually clearest between 25 and 50 per cent. Very common on large LCD televisions, where it is the main component of the dirty screen effect.
- Mura
- Irregular cloudy patches with soft edges, caused by small inconsistencies in the panel layers. Visible on a flat grey field and effectively invisible in ordinary content. Almost every panel has some.
- Corner and edge dimming
- A gradual falloff towards the edges, most obvious at 75 per cent and above. A gentle gradient is normal, particularly on edge-lit panels. A sharp step is not.
- Tint variation
- One region reading warmer or cooler than another across the same grey field. Common at the edges of large panels. Worth acting on only when you can see it in real content.
- A patch shaped like something
- If an uneven region has the outline of a taskbar, a logo or a HUD, you are looking at burn-in or retention rather than uniformity. Take that to the burn-in test.
What to do next
If something looks wrong, check it again in a normally lit room and from straight on, then check whether it appears on a second device. If it only happens on this screen and you are still inside the return window, that is the time to contact the retailer.
Questions people actually ask
What grey level is best for checking uniformity?
There is no single best level. Around 5 to 10 per cent shows clouding and backlight leakage, 25 to 50 per cent shows mura and banding, and 75 per cent and above shows edge dimming and tint drift. Run several and compare what each one reveals.
Is some unevenness normal?
Yes, on essentially every panel, and more so on larger ones. Uniformity is one of the hardest things to manufacture consistently. The question that matters is whether you can see it in the content you actually watch, from where you actually sit.
Why does the grid overlay exist?
To give you shared language. Saying the problem is in zone 3 of a nine-zone grid is far more useful in a support ticket than saying it is a bit to the left of the middle. The grid lines are thin and toggleable so they never contaminate the field itself.
Can this measure how uneven my screen is?
No. Measuring uniformity properly means taking luminance readings at a grid of points with a meter, which is what review sites do to produce those percentage figures. This gives you the field; the judgement is yours.