Black Screen
A plain black screen. Go full screen, then press Esc to come back.
Look over the whole screen for dots that stay a different color.
Use your monitor or phone controls to raise the brightness. To come back, press Esc or click Exit full screen.
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How to use this test
A full-screen black page. Use it to check an LCD for backlight bleed and clouding, to confirm that an OLED shows true black, to rest your eyes, or to spot dust and smudges on a dark surface.
Press Go full screen and turn off any room lights. Look at the corners and edges from a normal viewing distance. Press Esc or click Exit full screen.
What the results mean
On an LCD some glow in the corners is normal; large bright patches are clouding or bleed. On an OLED the screen should look switched off; a faint gray means the display isn't showing true black, often because of a picture setting. Colored dots on black are stuck sub-pixels.
Common questions
Is backlight bleed a defect?
A little is normal on almost every LCD. It becomes a defect when it's visible in normal content with the lights on. Warranty policies differ, so check the manufacturer's rules.
Does a black screen save battery?
On an OLED phone or laptop, yes, because black pixels are switched off. On an LCD the backlight stays on, so it makes little difference.
Why do I see a faint gray rather than black?
On an LCD the backlight always leaks a little. On an OLED check the picture mode and brightness limiter; some modes lift black levels on purpose.