What is a color screen test?
A color screen test fills your entire display with one solid colour, such as white, black, red, green or blue. With nothing else on screen, faulty pixels, dust, uneven backlight and colour tints become easy to see. It is the quickest way to check a new or second-hand monitor, laptop or phone.
How to test a screen for dead pixels
- Clean the screen so dust isn't mistaken for a pixel fault.
- Open the black screen and the white screen first, then come back and click the Red swatch to open it in full screen.
- Press the right arrow key or tap to step through red, green, blue and the other colours.
- Look for a dot that stays the same colour on every background: black means a dead pixel, a bright colour means a stuck pixel.
- Press Esc to leave full screen.
Which colour should I use?
| Colour | Best for |
|---|---|
| Black screen | Bright stuck pixels, dust and fingerprints, backlight bleed in a dark room |
| White screen | Dead (black) pixels, uneven brightness, using the screen as a light |
| Red, green, blue | Sub-pixel faults that only show in one colour channel |
| Gray | Uneven panels, banding and dirty-screen effect |
| Warm light | Soft, flattering light on your face during video calls |
How do I check a used monitor or laptop before buying it?
Open this page on the seller's device and spend two minutes on these checks. Everything runs in the browser, so nothing needs to be installed on their computer.
- Black screen in a dark room: look for bright dots (stuck pixels) and light leaking in from the edges or corners (backlight bleed).
- White screen at full brightness: look for black dots (dead pixels), yellow or pink patches and darker corners.
- Red, green and blue: a pixel that is missing in only one of these colours is a sub-pixel fault you would miss on a normal desktop.
- Gray: look for vertical or horizontal bands, smudges that move with the image, and burn-in from old logos or taskbars on OLED screens.
- Check the resolution: open Screen Resolution to confirm the panel really is the size the seller advertises.
What is backlight bleed, and is it normal?
Backlight bleed is light from an LCD's backlight leaking around the edges of the panel. It shows up as cloudy, lighter areas on a black screen, usually in the corners. A little bleed that you only notice on a full black screen in a dark room is common on LCD and IPS monitors. Bright patches that are visible in films or dark games are a defect worth returning. OLED screens have no backlight, so they don't bleed, but they can show burn-in instead.
Manufacturers have different policies on how many faulty pixels they replace under warranty, so test a new screen in the first days after delivery, while you can still return it easily.
Questions
What is the difference between a dead and a stuck pixel?
A dead pixel gets no power and stays black on every colour. A stuck pixel is always on in one colour, usually red, green or blue, and is most visible on a black screen.
Does this work on a phone?
Yes. On iPhone, Safari doesn't allow full screen for web pages, so the colour fills the page instead. Turn the phone sideways and hide the toolbar for the biggest area.
Can it fix a stuck pixel?
Sometimes a stuck pixel recovers after flashing colours for a while, but a dead pixel can't be fixed by software.
How do I get a white screen on my computer?
Open the White screen page and click Open white screen. It fills your display with white, with warm and daylight tones; press Esc when you are done. For black, use the Black screen.