Input Lag Input Lag

What input lag measures

Input lag is the time difference between when a video signal arrives at a display (TV or projector) and when that picture is actually displayed on the screen. It captures processing delay in the display's video pipeline, not how fast the picture changes once it starts to appear.

Reviewers isolate this from pixel response time using purpose-built measurement tools. RTINGS, for example, flashes a white square on screen and records the time until the display begins to change that square. The clock stops the moment the screen starts changing color, which explicitly excludes pixel response time (the color-transition itself) from the input lag figure. Response time and input lag are measuring different parts of the display pipeline entirely: response time is a pixel-level metric describing how long pixels take to change from one color to another, while input lag is a system-level delay covering the chain from signal arrival to displayed change.

The numbers: refresh rate and Game Mode

Refresh rate sets a hard floor on measurable input lag. On a 60Hz signal, the theoretical minimum measurable input lag is 8.33 ms; on a 120Hz signal, it is 4.17 ms. This reflects the duration of a single refresh cycle rather than actual processing speed. A measured input lag of 5.17 ms at 120Hz means only about an extra millisecond of real lag beyond the refresh-cycle floor. As a rule of thumb, 120Hz input lag should land around half the 60Hz figure for the same display, though it will not be exactly half in practice.

Game Mode reduces input lag by stripping out picture-processing steps (such as motion smoothing or extensive image processing) that add delay but aren't needed for interactive content. Auto Low Latency Mode (ALLM) automates this: a game console, PC, or other source device sends a signal to the display that causes it to automatically switch into a low-latency, low-lag mode for gaming. Once that signal is no longer present, the source disables it and the display reverts back to its previous picture mode, since aggressive latency reduction can compromise other image processing better suited to non-gaming content.

Real-world variation

Input lag varies significantly by picture mode on the same unit. Projector testing from ProjectorCentral has recorded input lag figures such as 24 ms for a Sony VPL-HW40ES, 34 ms for an Epson Home Cinema 8350, and 49.7 ms for a BenQ HT1075, each in that unit's best-performing (typically game) mode. Separately, ProjectorCentral notes that enabling frame interpolation can add more than 100 ms of input lag on its own, since interpolation requires additional frame analysis and buffering. Manufacturers do not typically publish input lag as a spec, so outlets like ProjectorCentral test every unit that comes through their office directly rather than relying on manufacturer-supplied figures.

Common confusions

Input lag and response time get conflated because both are millisecond-scale specs that affect how responsive a display feels for gaming, and both appear alongside each other in review data. DisplayNinja frames the distinction as response time being a pixel-level color-transition metric, versus input lag being a system-level delay from user input to displayed output. Though this framing is the outlet's own synthesis rather than a formal spec definition.

A labeled HDMI 2.1 port does not by itself guarantee low input lag at 120Hz. HDMI 2.1 provides the bandwidth and features (like ALLM and 120Hz signaling) that make low-latency operation possible, but the actual input lag figure still depends on the display's own processing pipeline and picture mode. Likewise, ALLM automates the switch into a low-latency mode but does not eliminate the underlying need for that mode to exist. It removes the manual step of toggling Game Mode, rather than removing Game Mode's processing shortcuts themselves.