Measured in milliseconds (ms), pixel response rate is the time it takes for a display pixel to change from black to white (black-to-white response time) or to transition from one shade of gray to another (gray-to-gray response time). The faster the pixel response rate, the better the monitor will be at displaying video without showing artifacts such as ghosting or blurring of moving images. Monitors with a fast 1ms gray-to-gray response are ideal for gaming, but even monitors rated at a 6ms gray-to-gray pixel response can show games without much blurring or ghosting. Most users won't notice input lag, which is the time it takes for the display to react to a command, but hardcore gamers consider it a key factor and typically seek out the fastest models (lowest lag time) available. The fastest monitor we've seen has an input lag of less than a millisecond, but for everyday apps, you can get by with 20ms to 25ms before lag becomes a noticeable problem.