What a white screen is good for
A pure white image (RGB 255, 255, 255) drives every pixel and every subpixel at full strength. Anything that blocks or dims the light stands out against it, which makes white the best colour for faults that stay dark.
Find dust under a laptop screen
Set the brightness to maximum and look at the white screen from a slight angle. Dust on the glass is sharp and wipes off with a dry microfibre cloth. Dust that got inside the panel looks like soft grey spots or hairs that stay put and do not wipe away. It is common on older laptops and after a screen repair. A repair shop can open the panel, but on a new laptop it is a reason to ask for a replacement.
Check uneven brightness and clouding
Look at the whole screen from your normal seat. LCD backlights are rarely perfect, so a slightly darker edge or corner is normal. Watch for clear bright clouds, dark bands, a yellow or pink tint in one area, or a visible pattern from the backlight. Take a phone photo at a normal exposure if you want to compare later or send it with a return.
Spot dark and dead pixels
A dead pixel shows as a sharp black dot on white. A stuck subpixel makes one dot look slightly coloured. For a complete check that also catches pixels stuck on, run the dead pixel test, which cycles through six colours and lets you mark each fault for a return.
Use it as a light for video calls
A bright white screen makes a soft, even light. Put it on a second monitor, a tablet or an old laptop just above your webcam, facing you, at full brightness. It fills in shadows on your face and can bring back a webcam frame rate that dropped in a dim room. Check the result in the webcam test.
Get a fair result
- Turn off Night Light, Night Shift, f.lux, True Tone and eye care modes. They tint the white yellow and hide colour problems.
- Turn off automatic brightness on laptops and phones so the screen does not dim while you look.
- Let a cold monitor warm up for 10 to 15 minutes. Backlights and OLED panels even out as they reach normal temperature.
- Look from your usual seat first, then from the side. Some unevenness only shows at an angle.
On a TV, open this page in the TV's browser or cast a browser tab, and switch the picture mode to Standard or Movie so dynamic contrast does not change the white.
Need black instead?
Use the black screen to check for bright stuck pixels, backlight bleed and IPS glow.
Questions
How do I make my screen completely white?
Press "Go full screen" above. The whole display turns pure white. Press Esc, or double click, to leave full screen.
Can I use a white screen as a light for video calls?
Yes. Put the white screen on a second monitor, tablet or laptop facing you, at full brightness and slightly above eye level. It works as a soft fill light and is enough to lift a dark webcam picture in a dim room.
How do I find dust under my laptop screen?
Show the white screen at full brightness and look at the panel at an angle. Dust inside the panel looks like small soft grey blobs that do not wipe off. Dust on the glass wipes away with a dry microfibre cloth.
Why does my white screen look uneven?
Most LCD screens are a little brighter in the middle and darker at the edges. Clear patches, a yellow corner or cloudy areas are called clouding or uniformity problems. Mild unevenness is normal; strong patches on a new screen are worth a return.
Why is my white screen yellow or blue?
Night Light, Night Shift, f.lux, True Tone or an eye care mode warm the colour. Turn them off before you judge the white. A blue tint is usually the monitor colour temperature set to cool.
Does it work on a phone?
Yes. iPhones do not allow full screen for web pages, so the white fills the browser window instead. Turn the phone sideways, and tap to show the Exit button.
More tests
Dead pixel testFull screen colours to spot dead and stuck pixelsBlack screenA full black screen, one clickRefresh rate testYour monitor Hz, measured in the browser
Mouse testCheck every button, side buttons and the scroll wheel
Keyboard testPress every key, with ISO, AZERTY and QWERTZ layouts
Controller testButtons, sticks, triggers and vibration for any gamepad