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Screen & Dead Pixel Tester

Fullscreen browser display diagnostics. Inspect dead or stuck pixels across 5 solid colors and estimate monitor refresh rate (Hz) in real time.

Dead & Stuck Pixel Checker

Inspect your display across five pure colors. Look for points that stay dark or bright as the background changes.

Choose a test color
Dead pixel: A point that stays dark on a light background.
Stuck pixel: A point that stays bright on a dark background.

How to Test for Dead Pixels and Screen Refresh Rate

  1. Launch Fullscreen Inspection: Click 'Launch Fullscreen Mode' to inspect pure colors without page scrollbars. If fullscreen is unavailable, the test fills the browser viewport; browser controls may remain visible.
  2. Inspect White Background for Dead Pixels: Examine pure white and light swatches. A dead subpixel transistor fails to draw power and stands out as an unresponsive black dot.
  3. Inspect Black Background for Stuck Pixels & Bleed: In a darkened room, inspect the pure black canvas for permanently illuminated red, green, or blue dots (stuck subpixels) and edge light leakage (backlight bleed).
  4. Cycle Colors & Observe Refresh Rate (Hz): Use Arrow Left / Right or click the canvas to cycle all 5 pure chromatic fields (Black, White, Red, Green, Blue). Monitor real-time Hz and frame consistency on the instrument gauge.

Display & Screen Troubleshooting Guide

What is the Difference Between a Dead Pixel and a Stuck Pixel?

A dead pixel is a permanently defective display element where all RGB subpixels fail to receive power, resulting in a black dot that never lights up. In contrast, a stuck pixel has one or more subpixels frozen in an active state, displaying a persistent red, green, or blue dot on contrasting backgrounds.

  1. Launch the Screen Tester and click the fullscreen launch button to enter true fullscreen mode.
  2. Cycle through solid color backgrounds: Black, White, Red, Green, and Blue by clicking or pressing the arrow keys.
  3. Inspect the white and light backgrounds closely for dark, unresponsive dots indicating dead pixels.
  4. Inspect the black and contrasting backgrounds for persistent bright dots (red, green, or blue) indicating stuck subpixels.
  5. If a stuck pixel is found, gentle pressure with a microfiber cloth or fast color cycling software can occasionally dislodge the stuck transistor.

How Does Browser Refresh Rate (Hz) Estimation Work?

APtester estimates screen refresh rate by calculating the precise millisecond delta between successive requestAnimationFrame cycles over a continuous sampling window. While highly accurate for measuring display animation smoothness and V-Sync sync rates (e.g., 60Hz, 120Hz, 144Hz), browser sandboxes cannot read physical display controller EDID hardware metadata directly.

  1. Open the Screen Tester on your target monitor without background browser tab throttling.
  2. Observe the live FPS and calculated display refresh rate (Hz) during the active sampling period.
  3. Ensure browser hardware acceleration is enabled in your browser settings (Chrome/Firefox/Edge) for accurate frame timing.
  4. Compare the measured rate against your operating system display settings (e.g. 60Hz, 120Hz, 144Hz, or 240Hz).

What Causes Screen Flickering and Backlight Bleed?

Screen flickering and backlight bleed occur from fluctuating display backlights, pulse-width modulation (PWM) dimming, or uneven bezel pressure along panel edges. APtester's fullscreen solid black canvas reveals backlight halos in dark rooms, while pure white and gray backgrounds expose subtle high-frequency luminance flickering and dirty screen effect (DSE).

  1. Darken your room completely and select the solid Black canvas in fullscreen mode.
  2. Observe the edges and corners of the panel for excessive white or yellow light bleeding through (backlight bleed / IPS glow).
  3. Switch to solid White or Gray to check for horizontal scan lines, panel flickering, or uneven brightness uniformity.
  4. If flickering persists across all brightness levels, check display cable connections (HDMI/DisplayPort) or update your GPU display drivers.

Technical Scope & Display Diagnostic Boundaries

100% Client-Side GPU & Display Processing: APtester renders all color buffers and measures frame synchronization deltas directly within your browser's local graphics pipeline. No screen captures, device identifiers, or display data are ever recorded or transmitted.

Browser Measurement Limits: Testing evaluates standard DOM requestAnimationFrame timing deltas. While highly precise for V-Sync frame rates, browser sandboxes cannot read hardware ASIC timing registers, panel overdrive voltage curves, or physical EDID cable metadata.

Frequently Asked Questions

Can a browser test fix dead pixels?

No tool can physically revive a dead pixel where the transistor has failed permanently. However, stuck pixels (frozen subpixels) can sometimes be unfrozen by rapidly alternating high-contrast primary colors.

Why does the refresh rate test say 60Hz on a 144Hz monitor?

If a 144Hz monitor measures 60Hz in the browser, your operating system display settings may be set to 60Hz, browser hardware acceleration is disabled, or energy saving mode is throttling window frame rates.

Why is true fullscreen required for dead pixel inspection?

Native fullscreen reduces browser distractions during inspection. If unavailable, viewport mode removes page scrollbars but browser controls may remain visible.