How to run a screen test
Clean the display gently, use its normal resolution, and turn off temporary color filters such as Night Light if you want a neutral visual check. Pick a starting color and press Start full-screen test. The page requests the browser’s fullscreen mode; if the browser refuses, it still covers the available page area. Move the pointer to reveal the controls, tap the open color area or use the arrow keys to move through the six colors, and inspect the whole panel at a comfortable brightness.
Repeat any suspicious area on several colors. A speck that disappears after safe cleaning was likely dust on the surface. A dot that stays dark on white and the RGB screens may be a non-lighting pixel; a colored dot that stands out on black may be a stuck subpixel. Gray is useful for noticing broad brightness variation or stains that pure black and white can hide. This is a visual comparison, not an automatic diagnosis.
What each solid color helps reveal
White lights all red, green and blue subpixels and makes dark dots, dust and dim patches easier to notice. Black makes always-lit or colored points easier to see and can reveal bright leakage near an edge in a dark room. Red, green and blue isolate the three primary subpixel channels, so a partial pixel problem may appear on one color but not another. Mid-gray is helpful for broader uniformity checks. The browser only asks the display to render these RGB values; the physical brightness and color you see still depend on the panel, operating-system profile, browser, viewing angle and room light.
A practical inspection example
Suppose a tiny cyan point is visible on black. Move through red, green and blue and note which screens make it disappear or change. Then leave the test and check the same location against normal content. This comparison can help you describe what you saw when consulting the manufacturer, but it does not determine warranty eligibility. As a second example, if a cloudy band appears only on dark gray at high brightness, repeat the check at the brightness you normally use and from your usual viewing angle before drawing a conclusion. Photographing a display can introduce moiré, focus and exposure artifacts, so treat a camera image differently from what you see directly.
Limits and safe use
This page does not measure color accuracy, gamma, refresh rate, response time, HDR performance or electrical condition. It cannot inspect pixels hidden under browser or operating-system controls, and browser fullscreen support varies. It does not repair stuck pixels and deliberately provides no rapid flashing sequence. Stop if a bright screen feels uncomfortable, avoid staring at maximum brightness, and follow the display maker’s care instructions. A visual difference is not proof of a hardware fault; software filters, cables, scaling, panel technology and viewing angle can change the appearance.
Frequently asked questions
How do I leave? Press Escape or reveal the controls and choose Exit test. If fullscreen was unavailable, Exit test returns to the normal page. Why are controls briefly visible? They provide a clear, accessible way to change color and leave; they fade so most of the panel remains unobstructed and reappear when you move or tap. Can this calibrate my monitor? No. Color calibration requires suitable measurement hardware and a managed workflow. Does it work on phones? Yes in a modern browser, although mobile browser bars or system gestures may reserve parts of the display. Can it certify a dead pixel? No. It only helps you inspect and record observations; check the device maker’s policy or a qualified technician for a decision.