Liquid crystals have a natural relaxed state. When a
voltage is applied they rearrange themselves to block certain
light waves. If left with the same voltage for an extended period of time (e.g. displaying a
pointer or a
taskbar in one place, or showing a picture for an extended period of time), the liquid crystals can develop a tendency to stay in one position. This ever-so-slight tendency to stay arranged in one position can throw the requested
color off by a slight degree, which causes the image to look like the traditional
"burn-in" on phosphor-based displays. The cause of LCD image retention is different from phosphor aging as in CRTs, but the visual phenomenon is the same: uneven use of display pixels. Slight LCD image retention can be recovered. When severe image retention occurs, the liquid crystal molecules have been polarized and cannot rotate in the electric field, so they cannot be recovered. The cause of this tendency is unclear. It might be due to various factors, including accumulation of ionic impurities inside the LCD, impurities introduced during the fabrication of the LCD, imperfect driver settings, electric charge building up near the electrodes,
parasitic capacitance, or a
DC voltage component that occurs unavoidably in some display pixels owing to anisotropy in the dielectric constant of the liquid crystal. ==Prevention and treatment==