The black pattern reveals fixed light leakage along the edges and corners. Near black helps when a display dims or turns off its backlight on a pure-black image. Dark gray shows clouding and uneven dark tones. Gray and white make bands, tinted areas, darkened edges, and brightness differences easier to see.
Backlight bleed is a fixed bright patch, streak, or cone near an LCD edge. IPS glow usually changes when you move your head or change viewing distance. Clouding appears as soft bright patches across a dark field. Local dimming can also create halos around bright objects; this is blooming, not backlight bleed.
This is a manual visual test, not a measurement. Judge the screen from your normal position and settings. A phone camera often exaggerates glow through automatic exposure, so do not use an overexposed photo as the only evidence. If a fixed bright area is visible in normal dark content, compare it with another unit or contact the manufacturer about its warranty criteria.
The test runs locally in your browser. It does not access a camera, files, or screen contents.
Prepare the room and display, start the test, and inspect each full-screen pattern after the hint disappears. Use the arrow keys, Space, Enter, number keys, a click, or a tap to switch patterns.
Backlight bleed usually stays in the same place when you move your head. IPS glow changes in brightness, color, or shape as the viewing angle and distance change.
Start with the brightness you normally use. Maximum brightness in a completely dark room is a stress test and can make normal panel characteristics look much more severe.
OLED screens do not have a separate backlight, so backlight bleed does not apply to them. The near-black and gray patterns can still reveal other panel-uniformity issues.