Dark streaks on most liquid crystal displays (LCDs) tend to be manufacturing defects. Although it is possible to experience temporary image retention on an LCD, this usually goes away with normal use. Dark streaks can plague any brand, visible when the screen displays a light-coloured background. Technically known as birefringent streaking, it is one of the most-noticeable and annoying LCD screen defects. Black streaks are possible on any sized LCD screen, from televisions to portable devices.
The screen layer components in an LCD must be perfectly aligned to prevent streaking. As light passes through the screen layers, it can "bounce" from the ridges in one layer off the ridges in another. This results in the light reflecting away from the viewer in certain patterns, resulting in a reduction in brightness along that pattern. This is a result of stresses in manufacture or shipping.
Glass Panel Inconsistencies
Glass panels that vary in thickness cause streaking as well. At the point where the glass becomes thinner, a reduction in white intensity is seen. This inconsistency can occur in any of the glass screen layers, causing streaking in wavy patterns or straight lines. This is a manufacturing defect, remedied by replacing the screen.
Dark streaks can manifest on the surface of the screen, through normal use. A variety of specialised screen cleaning fluids and wipes are available, designed to prevent the liquid from running into the device. When cleaning the screen, never use paper towels, since the fibres can and will scratch the screen. Use a microfiber cloth with distilled water or a specialised screen cleaner to remove the surface streaks.
Aspect Ratio Adjustment
Something often confused for a screen defect is the presence of a black line present on one or both sides of the LCD screen. Many television shows do not completely fill the screen, resulting in thin black lines on the edges. This is normal. It is remedied by pressing the "Zoom," "Format," or "Aspect" button on the remote. This keeps the screen filled with moving images, eliminating the black bars.