How to test a new monitor

Before you start

• Let the screen warm up for 15 to 30 minutes. Some effects, such as uniformity and colour, change as the panel reaches its working temperature.
• Set the native resolution and the highest refresh rate in the system display settings.
• Turn off night light, blue-light filters, automatic brightness and any dynamic contrast or eco mode, so you see the panel and not a filter.
• Set browser zoom to 100 percent and clean the screen gently with a dry microfibre cloth, so dust is not mistaken for a pixel.
• Check your retailer's return window and the manufacturer's pixel policy for that model before you start, so you know what counts for you.

1. Dead and stuck pixels

Open the dead pixel test in full screen and cycle through black, white, red, green and blue. Look across the whole screen from a normal viewing distance, then closer.

• A dot that stays black on every colour is a dead pixel.
• A dot that stays red, green or blue, or is wrong only on some colours, is usually a stuck pixel or subpixel.
• A dot that stays bright on black is a hot or bright pixel.

If you are not sure what you see, dead vs stuck pixel explains the differences and what can be done.

2. Uniformity, bleed and glow

• Run the monitor uniformity test with dark and mid greys. Look for patches, clouds, vertical bands or a darker corner.
• Run the backlight bleed test in a dim room. Light leaking from the edges that stays when you change your viewing angle is bleed; a glow in the corners that shifts with your angle is typical IPS glow.
• On mini-LED and other local-dimming screens, a small white object on black shows blooming: a halo around bright objects. Some halo is how these screens work; judge it at your usual brightness.

Judge with your eyes, not a phone camera, which makes dark scenes look far worse than they are.

3. Gradients, black and white levels

Open the gradient test. Smooth ramps without visible steps or colour stripes are what you want; some fine banding in dark grey is common, especially at 8 bit. Then the black level test shows whether the darkest and brightest steps are visible or crushed together, which often depends on picture settings and the RGB range rather than the panel.

4. Motion and refresh rate

• The monitor refresh rate test shows the rate your browser actually runs at. If a 144 Hz monitor shows 60, check the cable, the port and the refresh rate set in the system.
• The monitor ghosting test shows trails and overshoot behind moving objects; try the monitor's overdrive settings while you watch.
• If the monitor is overclocked, the frame skipping test checks whether every frame is really shown.

5. Touch screens and laptops

On a touch screen, laptop or phone, the touch screen test shows dead zones and how many fingers are registered. On a laptop, also check the screen while gently opening and closing the lid, which can reveal cable or hinge problems that come and go.

Used, refurbished and repaired screens

• Used OLED screens: show mid and dark greys full screen and look for shapes of taskbars, logos or game HUDs. See burn in vs image retention for how to tell temporary marks from permanent ones.
• Used LCD monitors: check uniformity and bleed carefully, and look for pressure marks or a yellow tint on white.
• After a screen repair or replacement: run the whole checklist, plus the touch screen test on phones and tablets. Look at the edges, where a badly seated panel often shows light leaks or dead touch zones.
• Buying in person: bring a laptop or phone, open the tests on the seller's screen and go through the pixel and uniformity steps at least. Five minutes on white, black and grey screens catches most visible defects.

Document what you find

1. Note what you saw, on which test, at which brightness and where on the screen.
2. Take a photo with the exposure lowered until it matches what you see, with the test colour clearly visible. Include something for scale near the defect if possible.
3. Repeat after a restart and on another device or cable if the problem may come from the source.
4. Contact the retailer or manufacturer with the notes and photos. Whether a given number of pixels or amount of bleed qualifies for a return depends on their policy for that model; no website can tell you that.