Fullscreen color tests for dead pixels and backlight bleed
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A dead pixel is a tiny dot on the display that never lights up — it shows as a permanent black speck on every color. A stuck pixel stays frozen on red, green or blue and is easiest to see when the screen is filled with the other two colors. Fill the screen with each pure color and look closely: any dot that doesn't match the fill is a defect. Dim the room and sit close for the best chance of spotting single-pixel faults.
The black fill is for backlight bleed — gray glows around the edges or corners, common on LCD panels. The white fill and mid gray reveal uneven brightness and dirty-screen effect (faint smudgy patches). The gradient makes banding visible: a healthy panel fades smoothly, while an 8-bit panel or poor processing shows visible stripes. The uniformity grid splits the screen into cells so you can compare brightness across regions.
One or two dead pixels is within most manufacturers' warranty tolerance, but check your warranty terms — some brands replace panels with even a single fault in the first year. Stuck pixels sometimes respond to pixel-fixing videos that rapidly cycle colors; success is not guaranteed and it won't revive a truly dead (black) pixel. On laptops, edge bleed that only shows in a dark room is normal for LCD and rarely a warranty issue; OLED panels can suffer burn-in instead, which shows as faint permanent ghosts on the gray and white fills.