CH 04 · Screen
White Screen Test
This white screen fills your display so you can check for dust, dead pixels, or uneven light. Choose a brightness step and timer to begin; nothing leaves your device.
A plain white page that fills the display. Press Start, then use the buttons at the top or the arrow keys to dim it in steps. A tap changes nothing, so it can lie on a table as a soft light.
- Look for dark pixelsOn a white field a dead pixel is a small black dot and dust is a soft grey spot. Clean the glass first, then look from an arm's length.
- Check evennessPatches that are yellow, grey or brighter at the edges are uneven backlight. The grey fields of the monitor test show it more clearly.
- Use it as a lightAt full brightness it lights a face for a video call or a page for a photo. Dim it in steps for a dark room. It is a soft light, not a lamp.
The screen stays awake while the page is open, where your browser allows it. The timer ends the session by itself. A tap on the screen changes nothing; the arrow keys step the brightness.
What the white screen checks
A plain white screen gives you one bright, even colour to look across. Dust or marks may stand out against it, and a pixel that stays dark or shows a different colour may be easier to notice. The test can also help you look for areas where the light seems uneven.
This is a visual check, not a measurement of display quality. The page cannot tell you why a spot looks different, and what you see can depend on the display brightness and the room around you.
Brightness, timer, and wake lock
The tool shows white across the screen and offers brightness steps. Change the step to see the white screen at another brightness level. There is no stated target level, so compare the same parts of the screen as you change it.
A timer lets you set how long the screen stays on for the test. A wake lock asks the device to keep its screen awake while the test runs. If the screen still turns off, the device may not allow that request or may not support it in the current setting.
What each result means
The main state is the full-screen white display. If it looks even, you may not see a visible issue in this check. That does not prove every part of the display works in every situation.
A dark spot, a spot with a different colour, dust, or a patch that looks dimmer or brighter is something you can inspect more closely. The page does not label a spot as a dead pixel or identify its cause. Brightness steps and the timer are controls, not pass or fail readings; the tool gives no numeric score or threshold.
When the screen looks wrong
First, look at the same area at another brightness step and check whether the mark stays in the same place. Make sure you are looking at the display itself, since dust or dirt on its surface can look like a screen defect. You can also compare the screen in a different room, because surrounding light affects what you see.
If a spot remains, note where it is and whether it stays dark, shows another colour, or changes with brightness. The result alone cannot show whether the cause is dust, a display issue, or something else. Check the device's display options or contact its maker or a repair service if you need help identifying the cause.
Browser support
| Browser | Runs |
|---|---|
| Chrome and Edge on a computer | Yes |
| Firefox on a computer | Yes |
| Safari on a Mac | Yes |
| Safari on iPhone | PartlyNo full screen on iPhone: the test fills the window instead. |
| Safari on iPad | Yes |
| Chrome on Android | Yes |
| Samsung Internet | Yes |
| Browsers inside apps | Yes |
Source: MDN browser-compat-data 8.1.8 · checked November 6, 2026
Questions
How do I use a white screen to check for dead pixels?
Open the full-screen white test and look across the display for a spot that stays dark or shows another colour. Change the brightness step and check the same spot again. This visual check cannot confirm the cause.
Can this white screen find dust on my display?
It can make some dust or surface marks easier to see against white. Check whether the spot is on the surface or appears to come from the display. The page cannot identify what caused a mark.
What does an uneven white screen mean?
A patch that looks brighter or dimmer may be uneven light, but this test does not measure the display or explain why the patch appears. Compare the same area at different brightness steps and in different room light.
Why does my screen turn off during the test?
The test includes a wake lock request to keep the screen awake. If the display still turns off, your device may not allow that request or may not support it in the current setting. The timer also controls how long the test stays on.
Is this a screen quality or hearing test?
It is a visual screen check for things such as dust, dark spots, different-coloured spots, or uneven light. It is not a formal display measurement, and it is not a hearing test.