If you just got a monitor, or you are still inside the exchange or return window, scan it once with solid colors on the day you set it up. This guide uses the «Dead Pixel & Refresh Rate Test» web tool and covers what to look for on which screen, and how to tell defects from dust or settings.
Prepare
- Wipe the screen with a dry cloth. Dust and dead pixels look alike at first.
- Keep brightness where you normally use it and turn off automatic features such as dynamic contrast or eco modes for now.
- Set Windows to the monitor's native (recommended) resolution. At other resolutions one pixel is drawn across several, and points can look blurred.
- A dark room helps when looking for backlight bleed.
1. Dead pixels — solid colors one by one
Most LCD pixels are made of three subpixels: red, green and blue. Press «Full-screen colors» and step through black → white → red → green → blue → gray, scanning the whole screen slowly.
| What you see | Suspect |
|---|---|
| A lone bright dot (white or colored) on black | A pixel or subpixel stuck on |
| A lone black dot on white | A dead pixel |
| A dot that differs only on red, green or blue | That one subpixel |
| A faint shadow in the same place on every color | Dust or debris — on the surface or inside the panel |
- If unsure, switch colors and see whether it stays in the same place. Dust looks like the same shadow on every color.
- Once you find one, keep that color on screen and take a close-up photo. It helps with an exchange request.
How many count as defective?
Pixel defects are covered by standards such as ISO 9241-307 (display test methods) and ISO/TR 9241-310 (specification and visibility of pixel defects), but whether a monitor is exchanged is decided by the maker's or seller's warranty terms. Many count not only the number but also the position (center or edge) and the type (stuck or dead), so compare what you found with the warranty document.
2. Banding — steps in a gradient
Banding is a smooth gradient breaking into visible stripes. With 8 bits per color there are 2⁸ = 256 levels, so a black-to-white gradient across a 2560-pixel-wide screen has steps about 10 pixels wide. Very faint stripes can therefore show even at 8 bits and are not a defect by themselves.
- In the tool's gradient box, the top is a smooth gradient and the bottom a 32-step staircase. If the top shows distinct stripes like the staircase, the settings are worth a look.
- Where to look: color depth, output format (RGB/YCbCr) and output range (full/limited) in the graphics driver's control panel, the monitor's picture mode (dynamic contrast, sharpness), and Windows HDR, night light or color profiles.
- When the cable, resolution and refresh rate combination hits a bandwidth limit, color depth can drop; compare with the refresh rate one step lower (depends on the equipment).
- Comparing the gray gradient with the RGB gradients shows whether one color bands more than the others.
3. Backlight bleed and clouding
- A black screen in a dark room shows light leaking at edges and corners. Higher brightness makes it more visible.
- On the 25% and 50% gray screens, look for cloud-like uneven brightness.
- Most LCDs bleed a little; it is a matter of degree. Judge whether it bothers you at normal brightness with normal content, and compare with the warranty terms.
4. Refresh rate — check Windows first
The tool's refresh rate is an estimate counted from how often the browser draws, so with several monitors, variable refresh (VRR) or power saving it can differ from reality. For the actual setting, go to Settings → System → Display → Advanced display, choose the monitor and check «Display information» and «Choose a refresh rate». If the rate you want is missing, look at the cable, port and resolution combination.
The moving bar (ghosting)
A long blurred tail behind the moving bar points to slow response (ghosting); a bar that jumps in steps points to skipped frames. Changing the monitor's overdrive level and comparing at the same speed shows which level smears less.
Sources
- Microsoft Support — Change the refresh rate on your monitor in Windows — Advanced display, display information, VRR
- ISO 9241-307:2008 — Analysis and compliance test methods for electronic visual displays — display test methods (paid standard)
- ISO/TR 9241-310:2010 — Visibility, aesthetics and ergonomics of pixel defects — specification and visibility of pixel defects (paid)
Published 2026-10-30