A bad pixel is a single pixel in a display panel that does not function correctly. It may be always on (bright white or a solid color), always off (black), or stuck on one subpixel color (for example, always red). These defects result from material flaws, manufacturing errors or mechanical damage.
Types include hot pixel (always lit), dead pixel (completely dark), stuck pixel (stuck on one color), and bright/dark dot (a point brighter or darker than the background).
The allowable number and type of bad pixels depend on the manufacturer and quality standards (e.g. ISO 13406-2, ISO 9241-307). In industrial or medical panels even a single defect may be unacceptable, whereas consumer displays may tolerate a few. Bad pixels are most noticeable on a uniform background and can reduce user comfort, though they do not necessarily indicate display failure.
