Background
Input lag: where the milliseconds go
When you click and wait for the screen to change, the delay you feel is the sum of many small delays: your own reaction, the mouse or keyboard, the computer, the wait for the next frame, and the display itself. Monitor reviews quote only the last part. The camera comparison above isolates the difference between two displays; the reaction test measures the whole chain.
Human reaction time
In laboratory studies, simple reaction time to a visual signal is typically around 180–250 milliseconds, averaging about 190 ms for young adults. It is faster with practice, alertness, and warm-up, and slower with fatigue and distraction. Online tests usually report higher numbers than lab studies, because the device chain adds its own delay on top.
Your results also vary from trial to trial. That is why the test uses several trials and reports the median, which is less affected by one slow or lucky attempt than the average.
The device chain
The total device delay on a gaming setup can be under 20 ms. On a TV in a movie picture mode with motion processing on, display processing alone can be far higher.
| Stage | What adds delay | Typical range |
|---|---|---|
| Mouse or keyboard | Polling rate: 125 Hz = up to 8 ms, 1,000 Hz = up to 1 ms; wireless and debounce add a little | 1–10 ms |
| Operating system and browser | Event handling, other apps, power saving | a few ms |
| Waiting for the next frame | Up to one refresh interval: 16.7 ms at 60 Hz, 6.9 ms at 144 Hz | 0–17 ms |
| Display processing | Scaling and image processing in the monitor or TV | under 5 ms on most monitors; much more on TVs outside game mode |
| Pixel response | Time for pixels to visibly change | under 1 ms (OLED) to several ms (LCD) |
What “input lag” means in monitor reviews
Reviewers use input lag for the display’s own part only: the time from the signal arriving at the monitor to a visible change on the panel. They measure it with a photodiode or a high-speed camera synchronized to the signal source, for example a Leo Bodnar lag tester. NVIDIA’s LDAT measures the full click-to-photon chain instead.
The photo comparison on this page is the older timer method that reviewers used before dedicated testers were common. It cannot give an absolute figure on its own, but with a reference screen of known lag it gets within about one refresh interval, which is enough to see whether a TV mode adds 10 ms or 100 ms.
Reducing the delay you can control
- On a TV, turn on Game mode or PC mode. It bypasses most image processing.
- Use the monitor’s highest refresh rate and a mouse polling rate of 500–1,000 Hz.
- Use a wired connection or a low-latency wireless receiver.
- In games, frame-rate limiters and low-latency modes such as NVIDIA Reflex or AMD Anti-Lag reduce queued frames.
Common questions
- What is a good score on this test?
- There is no target. Your score is your reaction time plus your setup’s delay, so the useful comparison is between your own runs: the same person, the same input method, and one setting changed, such as Game mode on and off.
- Why is my first trial slower?
- People usually react more slowly on the first trial while they get used to the task. The median of several trials reduces the effect of a slow first attempt.
- Does a 240 Hz monitor make me react faster?
- It shortens the wait for the next frame from up to 16.7 ms at 60 Hz to up to 4.2 ms at 240 Hz. That is a real difference, but small compared with human reaction time.