How to run the backlight bleed test
Bleed is faint, so the room matters more than the page. Turn the lights off or close the curtains, set the screen's brightness to the level you actually use, and give your eyes a minute on the black field before judging anything. At maximum brightness in a pitch-dark room nearly every LCD shows some light at its edges, so that setting tells you little about daily use.
Press Full screen so nothing else on the display is lit, then look at the middle of the screen from where you normally sit. Check each edge and corner in turn, then move your head left, right, up and down while you watch them. Step through the near-black and grey levels with a click, a tap or the arrow keys, and mark what you saw in the form under the test.
A photo is useful for a warranty claim, but phone cameras stretch exposure in the dark and make bleed look far worse than it is. Take it from your viewing distance, and compare it with what your eyes see before deciding anything from it.
Bleed, glow and clouding are different things
- Backlight bleed is light leaking past the panel's edges, usually where the frame presses on it. It shows as bright patches along an edge or in a corner, and it stays in the same place when you move your head.
- IPS glow is a bright, often silvery or warm haze in the corners of IPS panels seen at an angle. It shifts and changes strength as you move your head, and fades when you look at that corner straight on. It is a property of the panel type, not a fault.
- Clouding is uneven, blotchy brightness across the screen, from pressure or variation in the panel layers. It is easiest to see on the near-black and 50% grey levels, and common on VA and IPS panels.
OLED screens make light pixel by pixel and have no backlight, so they show none of these on black: a black OLED pixel is simply off. If you check an OLED, look at the grey levels for uneven brightness or tinted bands instead.
Local dimming can hide bleed
Full-array and mini-LED backlights dim zones behind dark parts of the picture, and many switch off altogether on a fully black screen. That hides bleed rather than fixing it. The black-with-a-dot level keeps a small grey square in the middle so the backlight stays on; if bleed only appears on that level, it will also appear in dark films and games with a bright element on screen. Zones far from the dot may still dim, so this check is a guide rather than a guarantee.
What the browser can and can't tell
A web page can set every pixel to black but has no way to measure the light your screen gives off, so this test can't detect bleed on its own. It shows the right patterns under the right conditions, and turns what you report into the summary.
The grey levels are code values: 2% grey is red, green and blue at 5 out of 255. How bright that looks depends on your display's gamma and settings, so on some screens 2% looks the same as black. That is black crush, a separate issue, and it can make bleed on the darkest levels harder to judge.
Questions
How do I tell backlight bleed from IPS glow?
Move your head. Bleed comes from light leaking at the panel edges, so it stays in the same place and keeps its shape whatever angle you look from. IPS glow depends on viewing angle: it changes strength and color as you move and mostly fades when you look at that corner straight on.
Is some backlight bleed normal?
A little is normal on almost every LCD, especially at high brightness in a dark room. What matters is whether you notice it in real use: bleed that shows up during dark scenes at your usual brightness is worth raising with the seller, while light only visible on a black screen in a pitch-dark room usually is not.
Can backlight bleed be fixed?
Sometimes it eases a little over the first weeks, and loosening the screws of a monitor's back panel slightly can reduce pressure on the edges, though opening a monitor can void its warranty. Lowering brightness makes it less visible. Bleed that is severe from the start is a manufacturing fault, and a replacement is the reliable fix.
Why does my photo show much more bleed than I see?
Phone cameras brighten dark scenes automatically, with long exposures and heavy processing, so faint light turns into bright patches. Lock the exposure or use a manual mode, shoot from your normal viewing distance, and compare the photo with what you see before relying on it.
Does an OLED screen have backlight bleed?
No. OLED pixels make their own light and switch fully off for black, so there is no backlight to leak. On an OLED, use the grey levels to look for uneven brightness, tinted bands or burn-in instead.
Why is there a small grey square on one of the levels?
Monitors with local dimming, such as mini-LED and full-array models, turn their backlight off in dark areas and often across the whole screen when everything is black. That hides bleed. The square keeps the backlight running so bleed and blooming have a chance to show.