Backlight Bleed Test

What Backlight Bleed Is

An LCD does not make its own light. Behind the panel sits a lamp that shines through it, and the panel works like a set of shutters that block that light to make the picture dark.

Those shutters are good but they are not perfect, and the frame around the panel cannot seal it completely. So on a fully black screen, a little light escapes around the edges instead of being blocked. That is backlight bleed: patches or streaks of lighter grey creeping in from the border of an otherwise black screen.

It shows up in exactly one situation — a dark scene in a dark room — which is why people find it while watching a film at night rather than while working. It is invisible the rest of the time.

OLED screens cannot do this at all, because every pixel makes its own light and a black pixel is switched off. If you have an OLED and you see light on a black screen, it is something else.

Backlight Bleed or a Bleeding Screen?

Before anything else, work out which of these you have, because they are unrelated and only one of them is harmless.

Backlight bleed is light leaking in from the edge of a black screen. It is even, it is soft, it has no hard border, and it does not change or spread over time. Most LCD panels have some. This page is about that.

A bleeding screen, which is what people usually mean when they say a laptop screen is bleeding, is physical damage. The panel has been cracked or pressed hard enough to break the layer inside it, and the liquid crystal has started to leak. It looks completely different: a dark blot, often black or purple with coloured edges, sitting in the middle of the picture rather than at the border. It has a definite shape, it spreads over days or weeks, and it usually appears after a drop, a knock, or something being closed inside the lid.

The test tells them apart in seconds. Backlight bleed only shows on a black screen and vanishes on a white one. A bleeding, damaged panel shows on every background, including white, because the damage is in the panel itself rather than in how it blocks light.

If yours is the second kind, nothing on the rest of this page will help. Leaked liquid crystal cannot be repaired, it does not stop on its own, and the panel has to be replaced. The one thing worth doing is acting sooner rather than later, because the blot grows.

Backlight Bleed or IPS Glow?

Most people who think they have found backlight bleed on a modern monitor have actually found IPS glow, and the difference decides whether it is worth returning the screen.

IPS glow is a property of how IPS panels work rather than a fault. Look at an IPS screen from an angle and the black turns into a pale silver haze, strongest in the corner furthest from your eye. Every IPS panel does this, including expensive ones. It cannot be manufactured away and no exchange will get rid of it.

Backlight bleed is a leak at the edge of a particular panel, so it varies from unit to unit and a replacement really might be better.

The way to tell them apart takes five seconds: move your head. IPS glow moves with you. Lean left and the glow shifts to a different corner, sit straight on and it shrinks. Backlight bleed stays exactly where it is no matter where you sit, because the light is escaping through a physical gap in the frame.

Glow also tends to be a wide, soft wash across a whole corner, while bleed is more often a smaller patch, a streak, or a bright spot right at the border.

So: it moves when you move, it is glow and it is normal. It stays put, it is bleed and it is worth judging on how much.

Is Backlight Bleed Normal?

Yes, some is. Almost every LCD panel ever made leaks a little light at the edges, and a screen with absolutely none is unusual rather than standard. Finding a small amount does not mean you were sold a faulty screen.

The honest test is not how it looks on a pure black screen in a blacked-out room at full brightness. That is the worst case you can build on purpose, and every panel looks bad under it. The test that matters is whether you can see it while doing what you actually do.

So put a dark film on, or a game with a night scene, at your normal brightness in your normal room. If you cannot pick the bleed out while the picture is moving, it is not a problem you are going to live with. If a bright patch pulls your eye away from what you are watching, it is.

Where it sits counts as well. A little glow at the very corner is what everyone has. A streak reaching well into the picture, or a bright patch along a whole edge, is a worse panel than it should be.

One thing worth knowing about a new screen: bleed sometimes settles slightly in the first few weeks as the frame and the panel relax. Slightly. Do not count on it fixing itself, and do not let it run past a return window on the hope.

What Causes Backlight Bleed

Almost all of it comes from how the screen was put together, which is why it varies so much between two units of the same model.

The panel sits inside a frame that has to hold it firmly without squeezing it. Screws done up a little too tightly, a frame a fraction out of true, or a panel pressing against its housing in one spot will all let light around the edge at that point. This is ordinary manufacturing tolerance rather than a defect, and it is the reason a review of a monitor can never tell you what your unit will look like.

Heat plays a part too. Materials expand, and a screen that runs warm for hours can show slightly more bleed than the same screen cold.

Handling causes the rest. A monitor dropped in transit, carried by its panel instead of its stand, or a laptop picked up by one corner of the open lid, can be knocked far enough out of true to open a gap. Pressing on the screen does the same thing, which is one more reason not to press on a screen.

What does not cause it: a cable, a driver, a graphics card, a setting, or anything you did with the software. Backlight bleed is mechanical, and nothing on the computer can change it.

Can Backlight Bleed Be Fixed?

Not really, and it is worth being blunt about that because plenty of pages suggest otherwise.

There is no setting for it. Brightness changes how obvious it is, and lowering brightness genuinely helps live with it, but the leak is still there. No driver, calibration or software has any effect at all, because the problem is a physical gap between a panel and a frame.

The advice you will find is to loosen the screws on the back of the bezel, or to press and rub the bright area with a cloth. The first occasionally helps a little and can also leave you with a panel that is no longer held properly, or a warranty that no longer applies. The second has no plausible mechanism behind it and risks damaging the panel, which is a far worse problem than the one you started with. Neither is worth it on a screen you can still return.

The realistic answer for a bad case is an exchange or a return. Bleed varies between units of the same model, so a replacement genuinely can be better, and this is the one screen fault where swapping is a reasonable thing to ask for.

For a mild case on a screen you are keeping, the practical fix is to stop looking for it. Lower the brightness a little, put a lamp on behind the screen so the room is not pitch black, and it will disappear from your day.

Backlight Bleed on a Phone or Tablet

The same test works on a phone: dark room, normal brightness, black screen, thirty seconds to adjust, then look at the edges.

What it means depends on the screen. An LCD phone or tablet — which includes the iPad, older iPhones and many cheaper Android phones — can leak at the edges exactly like a monitor, and a thin bright line along one side is the usual shape it takes.

On an OLED phone, which most current Android flagships and recent iPhones use, backlight bleed is not possible. There is no backlight to leak. If you see light on a black screen on an OLED, look for another explanation: the screen may simply not be showing true black because of a setting, or the light may be coming from around the glass rather than through it.

Screen bleeding on a phone usually means the other thing entirely — a cracked panel leaking, which spreads as a dark blot. On a phone that has been dropped or sat on, that is far more likely than bleed, and it is a repair rather than something to test around.

Why a White Screen Will Not Show It

People often go looking for a white screen for this test, and it is worth saying plainly that white cannot show backlight bleed.

Bleed is light escaping where the panel is meant to be blocking it. On a white screen the panel is not blocking anything — the backlight is meant to come through at full power everywhere — so a leak has nothing to stand out against. Black is the only background that works.

White is still useful, just for other faults. It shows dead pixels, dust, marks on the glass and uneven brightness across the panel. If you want to check a screen properly, do both: black for bleed and bright pixels, white for dark pixels and dust.

And as noted above, white does one thing here that black cannot. A mark that shows on white as well as on black is not bleed at all — it is damage in the panel.