Brightness Test — Free Online Test
The Brightness Test steps your display through evenly-spaced luminance levels so you can spot black-crush (loss of detail in dark tones), white clipping (loss of highlight detail), and non-linear brightness curves. It also helps you calibrate a comfortable working brightness for your ambient lighting — one of the biggest causes of eye strain is a display set too bright for the room. The test runs entirely in your browser, requires no colorimeter, and works on any laptop, monitor, tablet, or phone.
How to use the Brightness Test
- Sit in the room where you normally use the display, with your usual lighting.
- Start with brightness at 100% and open the Brightness Test.
- Cycle through the ten shade panels from black to white.
- Verify you can distinguish each panel from its neighbors — especially the near-black and near-white steps.
- Slowly lower your display's brightness until it feels comfortable for the ambient light.
- Re-run the test to make sure you can still see the darkest and lightest panels distinctly.
How to interpret your results
A well-calibrated display shows every step as distinctly darker or lighter than its neighbors. If the two darkest panels look identical, your display has black-crush — often caused by aggressive "dynamic contrast" modes. If the two lightest panels look identical, you have white clipping. Both problems can usually be fixed by disabling vivid/dynamic modes and using the panel's native color profile.
Common issues and what they mean
Black steps look identical
Disable dynamic contrast, HDR auto, and any "eye care" mode. Reset gamma to 2.2 in your GPU control panel.
Brightness feels uneven across the screen
This is backlight non-uniformity. Small variations are normal on laptops; large ones qualify for a warranty return.
Screen too bright at minimum brightness
On many laptops the minimum backlight is still bright. Try Windows Night Light, macOS True Tone, or a browser extension like DarkReader for evening work.
When to run this test
- When your eyes feel strained after long computer sessions.
- When editing photos or video and shadow detail looks wrong.
- After changing rooms or lighting conditions.
- Before a color-critical review or print prep.
Setting a comfortable brightness for your room
Eye strain from screens is usually a contrast problem rather than a brightness problem. If your display is much brighter than the wall behind it, your pupils constantly readjust between screen and surroundings, and that is what produces the tired, gritty feeling after a long session.
A practical target for typical indoor office lighting is around 120 cd/m². Rather than chasing a number you cannot measure without a colorimeter, use the paper test: hold a sheet of white printer paper next to a full-white screen. If the screen looks noticeably brighter than the paper, turn it down; if the paper looks brighter, turn it up. Repeat whenever the room lighting changes substantially.
In a dim evening room the target drops closer to 80 cd/m², which on most laptops is roughly 25 to 40 percent backlight. Warm-tinting features such as Windows Night Light and macOS Night Shift reduce blue output but do not reduce luminance, so use them in addition to lowering brightness rather than instead of it.
Black crush, white clipping and dynamic contrast
This test steps from pure black to pure white in evenly spaced increments. On a well-behaved display every step is visibly different from its neighbours. When the darkest two or three steps merge into a single black, the panel or its processing is crushing shadow detail; when the brightest steps merge, highlights are being clipped.
The most common cause on laptops is a vendor picture mode. Dynamic contrast, vivid mode, HDR auto-switching and eye-care presets all manipulate the tone curve in real time, and all of them can destroy detail at the ends of the range. Turn them off in the vendor utility and reset gamma to 2.2 in the GPU control panel, then re-run the test.
If the steps are still merged with all enhancement off, the limitation is the panel. Inexpensive TN and some VA laptop panels genuinely cannot resolve the darkest few percent. That is a specification limit rather than a defect, and it matters mainly for photo and video editing — which is why colour-critical work belongs on an external IPS or OLED display.
PWM flicker and why some screens cause headaches
Many displays dim by switching the backlight on and off very rapidly rather than by reducing current. That is pulse-width modulation, and at low brightness the off periods get longer. A significant minority of people perceive the resulting flicker as eye strain, headaches or a sense of visual fatigue that worsens the dimmer the screen gets.
The tell is counter-intuitive: symptoms get worse at low brightness, not high. If your eyes hurt more in a dark room with the screen turned down, suspect PWM. Confirm it by waving a pencil quickly in front of the screen at low brightness — a stroboscopic string of distinct images instead of a smooth blur indicates PWM.
Workarounds are limited but real: raise brightness above the PWM threshold (often 50 to 80 percent on affected panels) and reduce ambient light instead, or choose a display advertised as flicker-free or DC-dimming on your next purchase. Our PWM flicker guide covers how to identify affected models before you buy.
Frequently asked questions
What brightness level is best for the eyes?
A common target is 120 cd/m² for office work in normal indoor lighting, and 80 cd/m² for dim environments. Practically, set brightness so a full-white page feels no brighter than a printed sheet of paper next to the screen.
Does high brightness damage the display faster?
On OLED panels, sustained high brightness accelerates burn-in. On LCDs, it modestly shortens backlight life but is not harmful in normal use.
Why does my laptop dim automatically?
Adaptive brightness (Windows) or True Tone (macOS) responds to the ambient light sensor. You can disable both in Display settings.