Bright or stuck points
A subpixel that remains active may stand out as a fixed colored or bright point on pure black. Compare its coordinate across red, green, blue, and white before classifying it.
Five dark fields, one controlled sequence
Black Screen Test
The black screen test switches between CSS black and four near-black levels. Fullscreen removes ordinary site chrome; controls can be hidden and restored by touch or the C key while you scan for a bright point, edge glow, or broader dark-field irregularity.
Do more than open a blank page
How to use the black screen test
- Choose a realistic room and brightness. Dim reflections enough for dark-field inspection, but use a display brightness relevant to your normal dark-content viewing. The browser cannot change the physical brightness setting for you.
- Start on pure black. Enter fullscreen explicitly, hide the controls, and scan in a repeatable path. A fixed bright or colored point is easier to compare when visual clutter is removed.
- Move through 1%, 2%, 5%, and 10%. Near-black levels can reveal shadow-field banding, patches, tint, or transitions that are invisible on requested black. Swipe or use arrow keys to keep the comparison continuous.
- Change viewing angle separately. First observe from center, then move slightly. If a corner glow follows your position, record that rather than labeling it a fixed panel defect.
- Cross-check with another field. A suspected bright pixel should be compared on RGB and white. A broad LCD edge glow belongs in the dedicated bleed workflow.
Different observations on one surface
What the black screen test can help you inspect
LCD glow and bleed
Backlit LCDs may show bright edges, corners, clouding, or angle-dependent glow. A black field reveals the appearance but does not identify the assembly cause or severity.
OLED black behavior
Self-emissive pixels can turn off for requested black, but browser output still cannot measure black luminance. Near-black fields are useful for visible tint, banding, or processing comparisons—not an LCD backlight bleed claim.
Dark-field uniformity
Broad streaks or patches across low grey levels may indicate a uniformity observation. Temperature, compensation cycles, local dimming, viewing angle, and picture settings can affect the pattern.
Requested value versus emitted light
Why black screen test output is not a luminance reading
The black screen test asks the browser to render red, green, and blue channels at zero. An LCD may still have an illuminated backlight behind its liquid-crystal layer. An OLED can drive emissive elements differently, while display processing may alter how near-black values are handled.
Without a meter, controlled geometry, and known settings, the page cannot report candelas per square metre, contrast ratio, black crush, or shadow-detail accuracy. It can help you see and describe an obvious pattern under stated conditions, which is a narrower but still useful purpose.