Before you start
Set the room before the screen. Turn the lights down, close curtains and remove anything reflective from behind you. Dark-field faults such as backlight bleed and IPS glow are invisible in a bright room and grossly exaggerated in a completely dark one, so aim for dim rather than pitch black.
Set display brightness to the level you actually use, then note it. Almost every LCD shows some bleed at maximum brightness in the dark, which is why a test run at 100% brightness produces alarming results that mean nothing for daily use.
Clean the screen. A significant share of reported dead pixels are dust or dried droplets, and it is worth eliminating that possibility before spending twenty minutes on colour sweeps. Use a dry microfibre cloth, not a household cleaner.
Finally, set browser zoom back to 100%. Scaling changes how fine grid and gradient patterns are rendered, which can create artefacts that look like panel problems.
Run the check
Open the screen test and enter fullscreen so that no browser or system chrome remains on the panel. The fullscreen request has to come from a click, and once active the arrow keys move between patterns while F toggles fullscreen, so you can sweep without leaving the field.
Work through the solid colours in order: white, black, red, green and blue. White exposes dark pixels and dust; black exposes bright stuck pixels and backlight bleed; the primaries expose a pixel with one failed subpixel, which will only be visible on one or two of the three colour fields.
Mark defects as you find them. Pointer positions are normalised against the active pattern bounds, so a mark stays aligned when the window size changes and remains available after you leave fullscreen. Marking as you go is far more reliable than trying to remember three locations.
Move to the screen bleeding test for the dark-field inspection, because it fixes the pattern to black and records which brightness guidance level you used. Then, while the black field is up, move your head from side to side: a bright area that shifts with viewing angle is IPS glow, and one that stays put is bleed.
For an OLED panel, finish with the OLED screen test instead. Its colour cycle and timed run are designed for image retention rather than for pixel defects, and a static field on OLED should not be left up longer than the manufacturer recommends.
Read your result
A point that stays black on every colour field is a dead pixel. A point locked on one bright colour across every field is a stuck pixel. A point visible on only one primary is a single failed subpixel. These three need different responses, so the distinction is worth two extra minutes.
For dark-field results, judge at your normal brightness from your normal seating position. Bleed that is only visible at maximum brightness, from thirty centimetres away, in a fully dark room, is not a defect you will ever see in use, and no manufacturer will accept it.
Do not photograph the black field and judge from the photo. Camera exposure brightens dark areas far beyond what the eye perceives, which is why online galleries of "terrible backlight bleed" mostly show ordinary panels.
Measurement limits
The browser can display controlled fields; it cannot classify a physical panel defect. Colour management, operating-system scaling, browser zoom, panel overdrive and ambient light all change what appears, and none of them is visible to the page.
Uniformity cannot be quantified this way. Judging brightness variation across a panel requires a colorimeter and controlled conditions, so what you get here is a repeatable visual inspection, not a measurement.
A page cannot run a panel's own maintenance routine. Pixel refresh cycles on OLED televisions and monitors are firmware features, and displaying colours in a browser is not equivalent.
What to do next
Count the confirmed defects and compare them against the manufacturer's stated pixel policy, which is usually published and usually allows a small number before a panel qualifies for replacement. Knowing the threshold before you call saves a frustrating conversation.
If the panel is new and within a retailer's return window, a confirmed defect is worth acting on immediately rather than waiting for a warranty process, because return windows are short and warranty thresholds are strict.
If the only finding is mild corner glow at maximum brightness, the honest conclusion is that the panel is normal. Reduce brightness to a comfortable level and stop looking at black fields in dark rooms.
Symptom table
| Symptom | Likely layer | Next action |
|---|---|---|
| Dark point on every colour | Dead pixel or surface contamination | Clean the panel, then repeat the white field |
| Bright patch at one edge | Backlight bleed or IPS glow | Move your head while the black field is up |
| Fault visible on one primary only | Single failed subpixel | Confirm on red, green and blue in turn |
Common questions
How do I test a monitor for dead pixels?
Display fullscreen solid colours one at a time — white, black, red, green and blue — and look for any point that does not match its field. A dead pixel stays dark on every colour; a stuck pixel stays bright on every colour.
How many dead pixels before a monitor can be replaced?
That depends on the manufacturer's published pixel policy, which typically allows a small number of defective subpixels before a panel qualifies. Check the specific policy before starting a claim.
Is backlight bleed a defect?
Usually not. Nearly every edge-lit LCD shows some bleed on a black field at high brightness in a dark room. It only counts as a defect when it is visible at normal brightness in ordinary content.