In LCDs, since the source of light is always on, the concept of refreshing is not applicable. Response time refers to the time it takes the liquid crystal to change shape. Since changing the shape also changes the light passing to the screen, response time is defined in two alternative ways. Black-to-black response time refers to the time it takes the liquid crystal to switch from a shape that allows no light to pass (black) to a shape that allows all light to pass (white) and revert. Greyto- grey response time refers to the time it takes the liquid crystal to switch from any arbitrary shape to any other arbitrary shape, making a pixel change colour from one shade of grey to another. There is no common pair of shades of grey that is used by all manufacturers. Response time is usually mentioned in milliseconds.
Response time is an important factor that influences the display’s performance when dealing with fast-moving images. If the response time is greater than 16 milliseconds, there will, typically, be blurring and ghosting effects visible.