Input Lag and Response Time

Input Lag and Response Time

Input lag and response time are two different measurements that are often confused. Input lag is the delay between when you press a button or move your mouse and when the action appears on screen. Response time is how fast a pixel can change from one color to another. Both affect how responsive a system feels, but they are caused by different things.

Input lag comes from many sources. The mouse or keyboard has its own latency, the USB controller adds a small delay, the CPU and GPU take time to process the input and render the frame, the display connection adds a tiny delay, and finally the monitor itself takes time to show the image. Total system input lag is the sum of all these delays. For competitive gaming, every millisecond counts.

Monitor input lag is the delay between receiving a frame and displaying it. This is caused by the monitor's internal processing, like scaling, overdrive, and image enhancement. Gaming monitors have a dedicated gaming mode that bypasses most of this processing to reduce input lag. A good gaming monitor has less than 5 ms of input lag, while a TV might have 30 ms or more.

Response time is a property of the LCD panel itself. It measures how fast a pixel transitions from one color to another, usually from gray to gray. A slow response time causes ghosting, where moving objects leave a trail behind them. TN panels have the fastest response times, often 1 ms. IPS panels have improved to 1-4 ms. VA panels are the slowest, especially in dark transitions.

For competitive gaming, both input lag and response time matter. A monitor with low input lag but slow response time will have ghosting. A monitor with fast response time but high input lag will feel sluggish. The best gaming monitors combine both: under 5 ms of input lag and under 4 ms of response time. OLED monitors excel at both, with near-instant response times and very low input lag.