Backlight Bleed vs Dirty Screen: How to Tell in 5 Minutes

The short answer

Clean the screen first, then look at it on pure black in a dim room. Marks that change or vanish after a wipe were dirt. Light that sits fixed at the edges or corners on black is backlight bleed. A soft haze in the corners that moves or fades when you move your head is IPS glow, which is normal for that panel type. Blotchy grey patches across the middle of a plain grey screen, on a screen you know is clean, are the dirty screen effect (a uniformity problem in the panel, not dirt at all). Our backlight bleed test shows full-screen black and dark grey, and the dead pixel test has the mid grey and white screens you need for the rest.

What each problem looks like

• Dirt, smudges and residue: fingerprints, keyboard marks pressed onto a laptop screen when the lid closes, dried spray, dust. They are on top of the glass, so they look sharpest on a white screen and catch the light when you tilt the screen towards a lamp. They do not glow on black.
• Backlight bleed: light escaping from the LED backlight around the edge of an LCD panel, usually from frame pressure or loose assembly. It shows as bright patches along an edge or in a corner, it is easiest to see on black, and it stays in exactly the same place whatever angle you look from.
• IPS glow: a whitish, sometimes slightly yellow or bluish haze in the corners of IPS panels. It comes from the way IPS panels pass light at an angle, so it shifts, grows or fades as you move your head and almost disappears when you look straight at that corner from further back.
• Clouding: uneven, cloud-shaped lighter areas on black that are not tied to the edge. It is a backlight uniformity issue and, like bleed, it does not move with your head.
• Dirty screen effect (DSE): blotchy, smudge-like darker and lighter areas that show on a flat mid grey and when the picture pans, such as a hockey rink, a sky or a scrolling white document. It looks like a dirty screen, but cleaning does nothing, because the variation is inside the panel. Review sites see it far more on TVs than on monitors and laptops.

Step-by-step: test your screen in five minutes

1. Turn the screen off and clean it. Unplug a monitor, or shut a laptop down. Wipe gently with a soft, lint-free microfibre cloth. For stubborn marks, dampen the cloth (never the screen) with a little water, or on many laptops a 70% isopropyl alcohol wipe; Apple lists this for its displays, but check your own maker’s guidance, and never use cleaners with bleach, hydrogen peroxide or ammonia. Apple screens with nano-texture glass need the special cloth Apple supplies.
2. Look at it switched off. Tilt the screen towards a window or lamp. Anything you can still see now is on the surface, a scratch, or coating damage, not the backlight.
3. Set the room and brightness. Dim the lights, but not to total darkness for the first look. Set brightness to the level you actually use. Bleed is easiest to see at full brightness, so check there too, but judge the screen at your normal setting, because that is how you will use it.
4. Open the backlight bleed test and press Start full screen. The first screen is pure black. Look at all four corners and along every edge from your normal seat.
5. Move your head. Lean left and right, then up and down, about a foot each way. A patch that slides, swells or fades is IPS glow. A patch that stays locked to the same spot of the screen is bleed or clouding.
6. Tap through the darker greys. The test’s very dark and dark grey screens show clouding and uneven patches that pure black can hide.
7. Check the middle on mid grey and white. Open the dead pixel test and step to the grey and white screens. Blotches across the centre on grey, on a screen you have just cleaned, point to the dirty screen effect. Single dots on white or black are a pixel problem instead; the dead pixel vs stuck pixel guide covers those.
8. Watch real content. Play a dark film scene, a game menu or a night photo, then scroll a white web page. This tells you whether what you found matters day to day.

What the result means

• Marks gone after cleaning: it was dirt. On laptops, lines that match the keyboard keys come back if the keys touch the screen when the lid is shut; a thin cloth or keyboard cover stops that.
• Marks still there with the screen off: surface damage, a scratch, worn anti-glare coating or residue that needs another careful clean. No backlight test will change these.
• Corner haze that moves with your head: IPS glow. Every IPS panel has some, and it is not a defect. Sitting a little further back, raising room light slightly or lowering brightness makes it less visible.
• Fixed light at an edge or corner, only visible on black in a dark room: mild backlight bleed. Most LCD screens have a little. If you cannot see it in films and games at your usual brightness, it is not worth worrying about.
• Fixed light you can see in normal content, a bright patch towards the centre, or a strip along a whole edge: heavy bleed or clouding. This is the kind worth raising with the seller or maker.
• Blotches on mid grey and when scrolling: the dirty screen effect. Mild DSE is common panel-to-panel variation; strong DSE that you notice in sports, games or white documents is a fair reason to exchange a new screen.
• Nothing glows on black at all: either a very good LCD, or an OLED screen. OLED pixels make their own light, so OLED screens have no backlight to bleed and no IPS glow. On OLED, check for burn-in with the burn-in test instead.

Why photos make bleed look worse

A phone camera pointed at a black screen raises its exposure until the picture is bright, so faint bleed and glow look like floodlights in the photo. Judge the screen with your eyes, not the photo. If you need pictures for a warranty claim, use the camera’s manual or pro mode, lock the exposure low so the picture looks like what you see, and take every shot from the same distance at the same brightness. Show one straight-on shot and one from an angle, so the person reading it can see the patch does not move.

When to repair, return or replace

• New screen, inside the return window: if bleed, clouding or DSE bothers you in normal use, return or exchange it. Panels vary unit to unit, so a replacement of the same model can be much better. Do it early: return windows are short, and a maker’s warranty may only cover bleed it judges to be beyond normal.
• Monitor with bleed after mounting: pressure from a stand or wall mount that is screwed in too tightly can cause or worsen bleed. Loosening the mounting screws slightly is safe. Pressing on the panel, “massaging” the bezel or twisting the frame are not; they can crack the panel or void the warranty.
• Laptop with bleed that appeared after a drop or pressure on the lid: the frame or panel may be damaged. That is a repair, often a full screen replacement, so get a quote before paying for anything else.
• IPS glow: not a fault, and makers will not replace a screen for it. If it spoils dark films for you, a VA or OLED screen is the alternative next time.
• Buying a used laptop or monitor: run the backlight bleed test and the dead pixel test before you pay, in a shaded spot if you are meeting outdoors. Price mild bleed in; walk away from bleed you can see on a normal webpage. The laptop hardware test guide and the used laptop checklist cover the keyboard, battery, ports and the rest.

Spelling note: UK, Canadian and Australian readers write “grey”, “centre” and “microfibre”. The tests and the advice are the same everywhere.