Black screen
A full screen of pure black, sent to your display as sRGB 0, 0, 0 with nothing layered over it.
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Dimming changes what is sent to the panel, so this is no longer an exact colour value. Return the slider to 100% before judging anything.
What a black screen is for
Checking backlight bleed and IPS glow
An LCD makes black by blocking a backlight that is still switched on behind the panel, and any light that escapes around the edges shows up on a black field as a pale patch or a bright seam. That is backlight bleed. IPS glow is different: a silvery, warm sheen in the corners that shifts and fades as you move your head, caused by how IPS panels handle light at an angle. Bleed stays put when you move; glow does not. Check from straight on, at your normal viewing distance, in a room with some light in it. A fully dark room makes every panel look far worse than it is, and plenty of healthy monitors get returned on the strength of a photograph taken at midnight.
Seeing what your OLED actually does with black
On an OLED or a micro-LED panel each pixel makes its own light, so black means the pixel is switched off rather than masked. The result is a black that matches the bezel, with no glow and no visible edge to the picture. Put an OLED phone next to an LCD one on this page in a dim room and the difference is immediate: the LCD looks dark grey and slightly lit, the OLED looks like the screen is off. Because those pixels are genuinely off, they draw effectively no power, which is the mechanism behind dark-mode battery savings on OLED devices. How much you actually save depends on your panel, your brightness setting and how much of the screen is truly black, so treat any specific percentage you read elsewhere with suspicion.
Cleaning the screen
Dust, fingerprints and smears are far easier to see against black than against a bright desktop, because you are looking at light scattered off the surface rather than through it. Run this page, turn the room lights up, and work at an angle so the light rakes across the glass. Use a dry microfibre cloth first and only then a little distilled water or a screen-safe cleaner sprayed onto the cloth, never onto the panel. Avoid anything containing alcohol or ammonia on a matte or anti-glare coating, which can haze permanently.
Blanking a second monitor
A black full-screen page is a practical way to switch off a second display without unplugging it: useful when you are recording, presenting, or reading in bed and a bright panel in the corner of your eye is the problem. It also makes a clean, neutral backdrop for photographing small objects, and a distraction-free background behind a webcam.
How to run this test
- Turn the room lights down, but not off. A pitch-dark room makes every panel look faulty.
- Go full screen and let your eyes adjust for about thirty seconds.
- Look at each corner and edge in turn for pale patches or bright seams, then at the middle for cloudy blotches.
- Move your head from side to side. Glow that moves with you is IPS glow; light that stays put is backlight bleed.
- Look for any bright dot that stays in the same place. That is a pixel stuck on, not dust.
What a problem looks like
- Backlight bleed
- Irregular pale patches or bright bands, usually starting at an edge or a corner and pointing inwards. Common on LCDs and worse on panels with thin bezels. A small amount is normal; a bright wash across a quarter of the screen is not.
- Clouding
- Uneven blotches in the middle of the field rather than at the edges, looking a little like clouds seen from above. It comes from pressure on the panel stack and often shows up after shipping.
- Hot and stuck pixels
- A pixel stuck on shows as a bright white or coloured dot against black, and black is the easiest field to find one on. Move your head to make sure it is not a speck of dust sitting on the glass.
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
Why does my black screen look grey?
On an LCD that is normal: the backlight is still on and the liquid crystal cannot block all of it. If it looks unusually grey, check whether your display is set to a limited RGB range while your computer is sending full range, which lifts black off the floor. The black level test walks through that.
Should I test backlight bleed in a completely dark room?
No. A pitch-dark room exaggerates glow and bleed well beyond anything you would notice while using the screen, and it is the main reason people return perfectly normal monitors. Use a dimly lit room and judge it at your usual distance.
Does a black screensaver save power?
On OLED, yes, because black pixels are switched off and draw effectively no power. On an LCD the backlight stays on regardless of what is displayed, so a black screen saves almost nothing. Turning the panel off, or letting it sleep, is what saves power on an LCD.