Screen Brightness Test: Check Your Display Online

How to run the screen brightness test

Turn off auto-brightness first, so the phone does not change the screen while you test. Then look at the two rows of squares in the tool. The top row runs from 1% to 10% grey on a pure black background. The bottom row runs from 90% to 99% grey on pure white. Tap the faintest square you can still pick out in each row.

A well set up screen in normal indoor light lets you see the 2% or 3% square on black and the 97% or 98% square on white. If the first few dark squares vanish into the black, your brightness is too low for the room, there is glare on the glass, or the panel crushes shadows. If the light squares merge into white, the screen is too bright or the contrast is pushed too far.

What the full-screen tests show

Full-screen white fills the display with pure white at whatever brightness you have set. It is the quickest brightness check there is: slide your brightness to maximum and you see the most light the panel can give. It also shows yellow or pink tints, darker corners and pressure marks on LCD screens.

Colour test steps through white, black, red, green, blue and mid grey. Tap to move to the next colour. On each one, look for:

• Dead pixels: dots that stay black on the white, red, green and blue screens.
• Stuck pixels: dots that stay red, green or blue on the black screen.
• Backlight bleed: lighter patches at the edges of the black screen, common on LCD monitors and laptops.
• Uneven brightness or banding: blotches or stripes on the grey screen.
• Burn-in: faint shapes of keyboards, status bars or app icons left on OLED phones, most visible on grey.

Can a website read my screen brightness?

No. Browsers do not let websites read or change the brightness slider, which protects your privacy and battery. That is why this test shows you patterns to judge by eye rather than a brightness percentage. What the page can read is shown in the display panel: the screen resolution in physical pixels, the pixel ratio, whether the display supports wide colour (Display P3) or HDR, and the refresh rate your browser is drawing at.

Why does my phone screen look dim?

The usual causes, in order of how often we see them, are auto-brightness reacting to a bright room, battery saver mode capping the screen, a night or eye-comfort mode warming the colours, and an extra-dim or reduce white point accessibility setting. Phones also dim themselves when they get hot, for example in direct sun or while charging and gaming. If the full-screen white test still looks grey at full brightness with all of those switched off, the panel itself may be ageing.

Reading the refresh rate and resolution

Resolution is reported in device pixels, so a phone with a 412 by 915 point layout and a pixel ratio of 2.625 shows about 1081 by 2402. The refresh rate is measured by counting frames for one second. Many phones run at 60 Hz until you scroll, then switch to 90 or 120 Hz, and drop back to save power. Low power mode also caps the rate on many devices, so a reading of 60 Hz on a 120 Hz phone is normal when it is idle.