Why Online Color Vision Tests Can Be Wrong — Screens, Lighting, Night Mode
How monitor gamut and calibration, night mode and blue light filters, brightness, viewing angle, and ambient lighting change results — and the conditions for the most accurate check.
Printed test plates are designed to be viewed under standard lighting, and their print colors are controlled. A screen test can't guarantee those conditions. The same plate can look different depending on the device and its settings, so get to know the factors below before reading your result.
Settings that change results the most
- Night mode, blue light filters, “warm” color temperature: these reduce the screen's blue light and directly erase the color differences on blue-yellow (tritan) plates. If you missed many tritan plates, suspect these first.
- Color filters, color inversion, grayscale mode: accessibility color correction features change the plate colors. Turn them off during the check.
- Dark Reader–style browser extensions: extensions that force page colors can also affect canvas colors.
Differences between screens
- Gamut: Colorblind Lab computes colors assuming a standard sRGB screen. On a wide-gamut screen (DCI-P3, etc.) without color management, colors look more saturated, which can make plates slightly easier or throw them off.
- Brightness and auto-brightness: if the screen is too dim, small color differences disappear. Turn the brightness up and temporarily switch off auto-brightness.
- Viewing angle: some LCD screens shift color and contrast when viewed at an angle. Look at the screen straight on.
- True Tone and ambient light adaptation: features that adjust the screen's color temperature to the surrounding light also affect results.
Your surroundings and condition
- Warm yellow bulbs or reflections on the screen blur color judgment.
- Viewing too close draws your eye to individual dots, making the number harder to see. 50–70 cm (20–28 in) is about right.
- Results can get worse when you're tired or after long stretches of screen time.
A shared screenshot is not a test
Capturing a plate and sending it through a messaging app changes its colors through compression and color conversion. To have someone else try, send the link from “Copy result” (same seed) instead of a screenshot.
Conditions for the most accurate check
- 1. Turn off night mode, blue light filters, color filters, and dark-mode extensions
- 2. Raise screen brightness to 70% or more and turn off auto-brightness
- 3. Sit in daylight or under white lighting, with no reflections on the screen
- 4. Face the screen from 50–70 cm away and answer each plate within about 3 seconds
- 5. If the result is unclear, repeat with the same seed on another device
Limits of the simulator
The Machado (2009) model used by the simulator is an average model that expresses how far cone sensitivity shifts as a single severity value. Real experiences of color vision deficiency vary widely between individuals, and the tritan model has less evidence behind it than the protan and deutan models. Achromatopsia is approximated by removing color and keeping only luminance. Use the simulation as a tool for understanding “roughly how colors get confused.”