Arrange the room first
This is the part people skip and it decides the whole exercise. In daylight or under bright overheads, almost every panel looks flawless: ambient light washes out exactly the faults you are looking for. Backlight bleed is invisible in a bright room and obvious in a dark one.
You want the room dim enough that a black screen is the brightest thing in it, and you want to have been in that light for a minute or two so your eyes have adjusted. Judging a black field the second you walk in from sunlight is worthless.
Set the monitor to a normal brightness rather than maximum. Bleed at 100 percent brightness on a monitor you will run at 30 percent is not a fault you will ever see.
The patterns, in order
- Solid black, full screen, in the dim room. Look at the four edges and the corners. Light leaking inward from an edge is backlight bleed. A haze in a corner that changes as you move your head is IPS glow, which is a characteristic of the panel technology and not a defect.
- Still on black: look for bright coloured dots. Those are stuck pixels, and black is the background that reveals them.
- Solid white, full screen. Look for black dots, which are dead pixels, and for patches that are darker, warmer or cooler than the rest. Patchiness is a uniformity problem and it does not improve.
- Grey gradient. Look for visible steps instead of a smooth ramp. Some banding is normal, particularly on cheaper panels and over a cable running at a lower bit depth. Severe, obvious steps are worth asking about.
- One-pixel grid. Lines should be crisp and even. Shimmering, thickening or vanishing lines point at scaling somewhere: the monitor not running at its native resolution, a cable problem, or browser zoom, so check the browser is at 100 percent first.
- Checkerboard. A pattern that should be perfectly still but crawls or shimmers points at aggressive overdrive, which shows as inverse ghosting in motion.
- Colour bars. Look for bars that look muddy or that merge into their neighbour, which suggests the monitor's own picture settings have been pushed hard. Reset to factory settings before judging this one.
What is normal and what is not
| What you see | How common | How much it should matter |
|---|---|---|
| Corner glow that shifts with viewing angle | Normal on IPS panels | Not a defect. Every panel of that type does it to some degree. |
| Light leaking in from one edge | Common | Cosmetic for most work. Judge it at the brightness you will actually use. |
| Mild banding in a grey gradient | Common | Usually the cable or the colour depth, not the panel. Worth checking with a different cable. |
| One dead pixel near an edge | Common | Most people stop seeing it within a week. |
| Dead pixels in the centre of the screen | Less common | Genuinely distracting, and a fair reason to negotiate or walk. |
| Visible dark or discoloured patches on white | Less common | A uniformity fault. It does not improve and it cannot be calibrated away. |
| A permanent faint image of something else | Uncommon on modern LCDs | Image retention or burn-in. Walk away, and be especially careful with any panel used as a fixed display. |
Compiled by MyGearCheck from what each pattern reveals. The middle column describes how often these show up on panels generally; it is not a measured frequency and is not offered as one.
The checks that are not about the panel
- Every input. Bring the cable you will actually use and try each port; a dead HDMI port on an otherwise fine monitor is easy to miss and impossible to fix.
- The stand and the mount. Check the VESA holes are intact and that height and tilt adjustment still hold position rather than sagging.
- The buttons or joystick for the on-screen menu. If you cannot reach the settings, you cannot fix anything about the picture.
- Any buzzing or coil whine at different brightness levels, which is easiest to hear in the same quiet room you arranged for the black-field test.
- The power supply, if it is an external brick. A proprietary brick that is missing or failing can cost a surprising fraction of the monitor's value.
Bring your own laptop
Test the monitor from your own machine if you can. It removes an entire class of ambiguity: if a fault appears on your laptop and not on the seller's, the monitor is fine and their machine is not, and vice versa.
It also means you control the browser zoom, the resolution and the colour settings, which is the difference between reading a grid pattern and guessing at it.
Frequently asked questions
What is the difference between backlight bleed and IPS glow?
Bleed is light leaking in from the edges of the panel and stays where it is as you move. Glow is a haze, usually in the corners, that changes or disappears as you shift viewing angle. Glow is a property of the panel technology; bleed is a manufacturing variance.
How do I check for backlight bleed properly?
Solid black, full screen, in a dark room, at the brightness you will actually use, after your eyes have adjusted for a minute. Any of those conditions missing and the test tells you nothing.
Is colour banding a fault?
Usually not on its own. Banding often comes from the cable or the colour depth being negotiated rather than from the panel. Try a different cable before you treat it as a monitor problem.
Why do the grid lines look uneven?
Something is scaling the image. Check that browser zoom is at 100 percent and that the monitor is running at its native resolution. If both are correct and the grid still shimmers, the monitor's own scaler or sharpness setting is involved.
Should I worry about burn-in on a used monitor?
On an LCD it is uncommon but possible after long static use. On OLED it is the failure mode to check for above all others. Look for a faint permanent image on a mid-grey field, which is where retention shows most clearly.
Does a used monitor still have warranty?
Sometimes. Manufacturer warranties often run from the date of first purchase and are not always tied to the original buyer, so it is worth asking for the purchase date and receipt even second-hand.
Can I judge a monitor from photos in a listing?
Not for any of the faults above. A phone camera exaggerates bleed and hides banding, and a photograph of a black screen tells you more about the camera than about the panel. Insist on seeing it running.
How many dead pixels should make me walk away?
There is no universal number, and it depends far more on where they are than how many. One near the edge is a negotiating point. A cluster in the middle of the screen is a permanent distraction on a device you will look at every day.