Refresh Rate, 120Hz and VRR

Hertz is not frames per second

Two numbers get jammed together on spec sheets and in shop conversations, and keeping them apart clears up most of the confusion. Refresh rate, measured in hertz, is how many times a second the panel physically redraws whatever it has been told to show. Frame rate is how many genuinely new pictures the source hands over: the Blu-ray, the stream, the console. A television can refresh at 120Hz all day while a film feeds it only 24 fresh images a second. The screen is busy; the story is not moving any faster.

That gap is the whole subject. A higher refresh rate gives the panel room to do things (hold each frame for less time, insert frames of its own, sync itself to a wandering game) but it never invents detail the source didn’t send. Working out what fills that room is how you tell a real motion improvement from a sticker.

Why 120Hz helps games but not film detail

Games are the clean case. A console or PC that renders 120 frames a second, fed to a 120Hz panel, shows you 120 distinct moments of play every second. Movement is smoother, aiming feels more connected, fast camera swings stay legible. The refreshes do real work because the source actually filled them. None of it arrives, though, unless the connection can carry it. 4K at 120Hz needs the bandwidth of HDMI 2.1; the same panel wired to an older HDMI 2.0 port is capped at 4K60, so the socket you plug into matters as much as the panel behind it.

Film is where the marketing quietly overreaches. A 24fps movie contains 24 images per second and not one more, so a 120Hz screen cannot add sharpness that was never shot. What it can fix is cadence. 120 divides evenly by 24, so each film frame is held for exactly five refreshes. A steady 5:5 beat. A 60Hz set can’t manage that: 60 isn’t a multiple of 24, so it falls back on 3:2 pulldown, showing one frame for three refreshes and the next for two. That uneven rhythm is judder, and it is ugliest on slow horizontal pans.

So 120Hz earns its keep on film not by adding anything, but by removing a flaw that 60Hz forces on you.

There is a second route to smooth-looking film, one where the set invents brand-new frames to slot between the real ones, but that is a different trade with side effects of its own.

Sample-and-hold blur and the black-frame trick

Old tube TVs flashed each frame in a brief pulse and left the screen dark between them. Flat panels do the opposite: they hold each frame lit until the next one replaces it. This is sample and hold, and it creates a blur that has little to do with the panel’s response time. As your eyes smoothly track a moving object, they keep gliding while the held frame sits still, and that static image smears across your retina. The faster the panel swaps frames, the shorter the smear, a second, quieter reason higher refresh looks better in motion.

The catch is that the returns shrink: moving from 60Hz to 120Hz roughly halves the persistence blur, but wiping it out by speed alone would take a refresh rate far higher than anything on sale, which is exactly why some sets reach for strobing instead.

It also explains something that surprises people: an OLED, whose pixels switch almost instantly, still blurs a moving object. Its pixels aren’t the bottleneck; the held frame is.

Some sets attack the blur head-on. Black-frame insertion drops a dark frame between the real ones, and backlight scanning strobes the light off briefly, both mimicking the crisp motion of a strobed tube TV. It works, but you pay in brightness, and the flicker can bother sensitive eyes, the same PWM-style pulsing that gives some people headaches. How the backlight is built and dimmed feeds straight into this, which the backlight and local-dimming page covers in depth.

VRR: G-Sync, FreeSync and the tearing problem

Fixed refresh rates and live games disagree by nature. A game’s frame rate lurches around with the scene (ninety frames one second, forty-eight the next) while a plain panel keeps redrawing on its own fixed schedule. When a fresh frame lands halfway through a refresh, the screen shows the top of the old image and the bottom of the new one at once: a torn seam across the picture. Force the two into step with old-fashioned v-sync and you trade the tear for stutter and extra lag.

Variable refresh rate solves it from the other end. Rather than make the game wait, the panel waits for the game, redrawing the instant each frame is ready. AMD’s FreeSync, NVIDIA’s G-Sync and the HDMI 2.1 VRR standard are three routes to the same behaviour, and most recent sets speak at least one of them. VRR works inside a range of frame rates; drop below the floor and low framerate compensation repeats frames to stay in bounds. It isn’t flawless, some panels shift brightness slightly as the rate changes, a dark-scene shimmer known as VRR flicker, but for anything with an unstable frame rate it is the single biggest smoothness upgrade on offer.

Input lag, game mode, and the numbers on the box

For players, one figure outranks every picture setting: input lag, the delay between pressing a button and seeing the result. All the processing that flatters a movie (interpolation, noise reduction, heavy upscaling) takes time, and time is lag. Game mode switches most of it off, and Auto Low Latency Mode lets a console flip the TV into game mode by itself, so you can’t forget. Pair that with VRR and a source that can keep up, and the set finally feels responsive.

Which leaves the numbers printed on the box, and most of them are noise. A panel is natively 60Hz or 120Hz; that is the fact worth knowing. The badges, “Motion Rate 240,” “Clear Motion 200,” and every similar invented index: blend the true refresh with backlight strobing and interpolation into a bigger, meaningless figure. A “240” sticker routinely rides on a 120Hz panel, occasionally a 60Hz one. The number worth hunting for is the native refresh rate, buried in the detailed specs; treat anything larger as decoration.

For how that panel then gets driven by the whole processing chain, the motion and video-processing overview picks up the thread.