Monitor Test & Dead Pixel Test

The easiest way is with a browser-based monitor test like this one. Choose one of the six tabs above: Dead Pixels, Hz & FPS, Resolution, Ghosting, Backlight or Banding. For the pattern tests, start the full-screen test, switch patterns with the arrow keys, a click or a tap, and press Esc to exit. Hz & FPS and Resolution display the values directly. On a phone, tap to switch colors. On an iPhone, browsers do not offer true full-screen mode, so the browser bars may remain visible. To test a TV, connect a computer via HDMI. The test runs entirely in your browser, with no download or account, and nothing is uploaded.

The test fills the screen in turn with red, green, blue, white, black, yellow, cyan, magenta and a color gradient. A dead pixel stays dark and appears as a black dot on light backgrounds. A stuck pixel always lights up in one color and stands out against black: A red, green or blue dot on the black screen is usually a stuck subpixel. If just one subpixel fails, the pixel shows the mixed color of the other two on white, for example a magenta dot when green is missing. This works the same way on LCD and OLED screens. Clean the screen first, as dust can look like a dead pixel.

That depends on the standard and the manufacturer. Many manufacturers still refer to pixel defect class II under ISO 13406-2 (now superseded by the ISO 9241-300 series): up to 2 permanently bright pixels, 2 permanently dark pixels and 5 defective subpixels are permitted per million pixels. For Full HD with 2.07 million pixels, that works out to roughly 4 bright and 4 dark pixels. Whether a defective pixel is covered by warranty depends on the manufacturer's or seller's warranty terms; some guarantee zero defective pixels. Check the terms before making a claim, and document each defect with a photo, its color and its position.

A stuck pixel sometimes disappears after a few hours of rest or on its own, but a dead pixel is permanently defective. There are no guarantees. Be careful with guides that tell you to press on the panel or use flashing videos: They can damage the display, and rapid flashing can trigger seizures in susceptible people. This test therefore does not flash or fix pixels; it makes them visible. If you find defective pixels during the warranty period, contact the manufacturer or retailer and include photos from the test.

Open the Hz & FPS tab. The browser draws at most once per refresh cycle. The test measures the time between two draw calls and converts it to Hertz: 6.94 ms per frame is 144 Hz, 16.67 ms is 60 Hz, and 4.17 ms is 240 Hz. Using the median makes the measurement resilient to occasional hiccups. The 5-second measurement also shows jitter and dropped frames. The result applies to the monitor displaying the window. Hz tells you how often the monitor can show a new image each second; FPS tells you how many frames your computer renders. The tab shows both values, but it is no substitute for a game benchmark.

Usually, the higher refresh rate hasn't been selected. In your system's display settings, check under advanced display or refresh rate whether 144 or 165 Hz is selected. Other possible causes include a cable or port that doesn't support the rate (older HDMI versions), a laptop power-saving mode that limits the browser to 60 Hz, or a window on the wrong monitor. Variable refresh rates such as G-Sync or FreeSync can also produce different readings.

In the Ghosting tab, a high-contrast block moves across a gray, black or white background at 240 to 1920 pixels per second. Follow it with your eyes: A light or dark trail behind it is ghosting. Motion tests like this are often called UFO tests; this test does not measure response time in milliseconds. To check for backlight bleed, open the Backlight tab in a darkened room: Bright patches along the edges and corners of the black screen that stay in the same place are backlight bleed. A glow that changes with your viewing angle is IPS glow and is normal for IPS panels. OLED panels have no backlight, so they cannot have backlight bleed.

The Resolution tab combines the screen size in CSS pixels with the scaling factor. A laptop with 1536 × 864 CSS pixels at 125 % scaling has 1920 × 1080 physical pixels. The test identifies common resolutions such as Full HD (1080p), WQHD (1440p) and 4K UHD (2160p). Enter the diagonal in inches to calculate pixel density: A 27-inch monitor with 2560 × 1440 pixels has 108.8 PPI. Set your browser zoom to 100 %, or the result may be inaccurate. If you have multiple monitors, the result applies to the one displaying the window.