Dead pixel types and how to spot them
There are three types of pixel defects: dead pixels (permanently off — appear as black dots on light backgrounds), stuck pixels (permanently on in one color — appear as bright red, green or blue dots) and hot pixels (always white). Dead pixels are easiest to spot on a white screen, stuck pixels on a black screen. To test properly, display a solid color at fullscreen, set your room lighting to normal (not too dark, not too bright), and scan the screen systematically in rows from about 30cm away. Check white, black, red, green and blue — each color reveals different defects.
LCD monitors have a backlight behind the panel that can leak around the edges, creating brighter patches visible on dark content.
LCD monitors have a backlight behind the panel that can leak around the edges, creating brighter patches visible on dark content. IPS panels have a related issue called IPS glow — a warm-toned brightening that shifts as you change viewing angle. To test, display a full black screen in a completely dark room at 50-75% brightness (max brightness exaggerates the effect). Some bleed and glow is inherent to LCD technology and is not a defect. It becomes a problem only when bright patches are visible at normal viewing distance during regular use — dark movie scenes are a good real-world test.
Color uniformity testing
Display a solid medium gray at fullscreen and look for any patches that appear warmer, cooler, brighter or darker than the surrounding area. Uniformity issues are caused by uneven backlighting or panel manufacturing variance. Check from your normal seating distance — slight variations visible only at close range are generally acceptable. If a section of the screen has a visible pink, green or yellow tint compared to the rest, the panel has a uniformity defect. This matters most for photo editors, designers and video colorists.
When to calibrate your monitor
Most consumer monitors ship with acceptable default calibration for general use. Calibration becomes important when colors need to be accurate for professional work — photo editing, graphic design, video production or print proofing. Hardware calibrators (colorimeters) produce the best results, but software calibration using built-in OS tools (Display Settings on Windows, Display Calibrator Assistant on Mac) can correct obvious issues like color temperature bias or gamma shift. The color screens in this tool can help identify calibration problems but cannot replace a proper calibrator for professional work.
Testing phones and tablets
Phone and tablet screens develop defects too — especially after drops, pressure damage or water exposure. The testing process is the same: display solid colors at fullscreen and look for dark spots, bright spots, color shifts or lines. On OLED phones, also check for burn-in by displaying a solid gray screen and looking for faint shadows of frequently-displayed UI elements (status bar, navigation buttons, keyboard outline). OLED burn-in is permanent and progressive — catching it early helps you manage which apps or interfaces you leave on screen for extended periods.
What to do when you find defects
If you find dead pixels on a new monitor, check the manufacturer's dead pixel policy — most offer replacement if the number exceeds their threshold (usually 3-5 bright or dark subpixels). Document defects with close-up photos showing the pixel location on a solid-color background. For stuck pixels, try running a pixel-cycling tool (rapidly flashing colors) on the affected area for 20-30 minutes — this works about 50% of the time. For backlight bleed, only return the monitor if the bleed is visible during normal use at normal viewing distance. Some panel variance is expected, and a replacement may have similar or different uniformity issues.