How to check a monitor or laptop screen before the return window closes
The short answer
Check the screen the day it arrives. Clean it, set brightness to maximum, open a fullscreen colour test and look across solid black, white, red, green, blue and grey. A dot that is black on every colour is a dead pixel, a white one is a hot pixel, and a coloured one is stuck. Then view black in a dark room for backlight bleed. Mark and photograph every fault before you contact the seller.
A screen fault is cheapest to deal with on the first day. Inside the return window a retailer will usually take a screen back without an argument. After it, you are relying on the maker’s warranty, and that often allows a few faulty pixels before a panel counts as defective. In the EU the legal minimum for an online purchase is 14 days, and many shops give no more than that, so the check should not wait for a free weekend.
This is the whole check. It takes about ten minutes.
Before you start
- Clean the screen. Use a dry microfibre cloth. Most “stuck pixels” are dust.
- Let it warm up for a few minutes, and set brightness to maximum.
- Turn off anything that changes colour: night mode, auto-brightness, and any eye-comfort setting.
- Use the native resolution. Scaling blends a faulty pixel into its neighbours and can hide it.
Step through six colours
Open the dead pixel test and press Go fullscreen. Tap, click or press a key to move through black, white, red, green, blue and grey. On each one, look across the whole screen from about arm’s length, corners and edges included.
| What you see | What it is | Best colour to spot it |
|---|---|---|
| A black dot on every colour | Dead pixel | White |
| A white dot on every colour | Hot pixel | Black |
| A red, green or blue dot that vanishes on its own colour | Stuck pixel | Black, then the primaries |
| A soft speck that shifts as you move your head | Dust on the glass | White |
| A lighter patch at an edge, on black | Backlight bleed | Black, lights off |
| Cloudy or uneven areas | Poor uniformity | Grey |
When you find something, press and hold on it to put a numbered ring around it. With a mouse, right-click or Shift-click; from the keyboard, press M with the pointer over the spot. Marking the same place twice removes the ring. The ring is hollow, so the pixel stays visible inside it for a photograph.
Check black in a dark room
Pixels are only half of it. Turn the room lights off, stay on the black field and look at the edges and corners.
- Backlight bleed is light leaking around the edge of the panel. It stays in the same place when you move your head.
- IPS glow is a pale sheen in the corners that shifts and fades as you change your viewing angle. It is a property of the panel type, not a fault.
- Clouding is uneven patches in the middle of the screen. The grey field shows it best.
A little bleed is normal on an LCD. Bleed you can see from your usual seat with a film playing is worth returning. OLED screens have no backlight, so on one of those, check grey for a colour tint and for faint ghosts of old images instead.
What counts for a return
Inside the retailer’s return window, you generally need no threshold at all: “it has a dead pixel” is enough. That is the reason to check now.
After that, the maker’s warranty applies, and many makers work from the fault classes in ISO 9241-307, which took them over from the older ISO 13406-2. Most consumer screens are sold as Class II:
| Screen | Pixels | Always lit | Always dark | Sub-pixel faults |
|---|---|---|---|---|
| 1920 × 1080 | 2.07 million | 4 | 4 | 10 |
| 2560 × 1440 | 3.69 million | 7 | 7 | 18 |
| 3840 × 2160 | 8.29 million | 16 | 16 | 41 |
Those are the numbers the standard permits, which is more than most people would accept. Some makers promise better, such as a replacement for a single bright pixel, so read the pixel policy for your exact model before you write to them.
Record it
When you leave fullscreen, the test lists every mark by position, for example “top left, 12% across, 8% down”, with an approximate pixel coordinate. Copy result puts that on the clipboard as plain text. Nothing is stored or sent; close the tab and it is gone.
Add a photograph of each fault on the colour that shows it best. Hold the phone square to the screen and tap to focus on the pixel. Then send both to the seller the same day. A dated message inside the window is what protects you if the reply is slow.
If the pixel is stuck rather than dead
A stuck pixel sometimes frees itself. The test has a Try to fix a stuck pixel mode that flashes the colours four to five times a second and stops by itself after five minutes. It shows a flashing-light warning first: do not run it if anyone who can see the screen is sensitive to flashing light, and there is no need to watch it. It does nothing for a dead pixel, and it is not a reason to let a return window run out.
Buying used
The same check works at a seller’s table. Ask to open one web page, go fullscreen and step through the colours; it takes two minutes and installs nothing. While the laptop is open, the keyboard test finds dead keys, and a webcam check covers the camera. The laptop check strings every test together, adds ports and battery health, and prints a record; how to check a used laptop explains each step. There are screen-specific notes for a laptop, a phone and a TV.
- Screens
- Buying
