A dead pixel test is a test which is conducted to see if a display has a dead pixel or dead subpixel. The test can identify pixels which are stuck on as well as pixels which are permanently off. Several websites have an in-browser dead pixel test which can be used to run a quick check. It is also possible to download software, which is often available as freeware, for dead pixel testing. One advantage of downloading software is that it works on and offline, and it may have more options.
A completely dead pixel will display as either a black or white spot in the screen. In other cases, one of the red, green, or blue subpixels is damaged, but the other two are functional, so a pixel can look odd sometimes but not all of the time as a result. Using a dead pixel test, people can identify broken pixels in their screen.
The test displays a flat color which fills the entire screen. Black and white displays are used to check for whole dead pixels. Blue, green, and red displays can be used to search for damaged subpixels which may not show up as well against white or black. The dead pixel test can be used on a laptop, desk top, mobile phone, digital television, or any other type of device with a display which uses pixels. Some allow people to flash the display because sometimes cycling quickly will resolve a stuck pixel so that it will display properly.
People have a number of reasons to check for dead pixels. If the product is still under warranty, they may be able to get the manufacturer to replace it. However, manufacturers are often reluctant to replace products with a single dead pixel or a small cluster, arguing that it's a statistically acceptable defect. If there is a large grouping of dead pixels or an unusual number, the manufacturer may be more willing to address the issue. It certainly doesn't hurt to contact a manufacturer about a dead pixel on a product which is still under warranty.
Checking for dead pixels can also resolve confusion about strange marks on the display. While the eye is very good at gliding over a dead pixel, over time it can become a faint source of irritation, especially if it has not been identified. There may also be cases in which a dead pixel legitimately interferes with operation of the device and it is necessary to identify it with a dead pixel test so that users can be aware of it.