Watch high-contrast blocks glide across the screen — if they drag shadowy trails or bright halos behind them, your display's pixels are struggling to keep up. Runs right in the browser, nothing to install.
Follow the blocks with your eyes — a faded trail behind them is ghosting, a bright halo is overshoot.
Watch the moving blocks above: on a fast screen their edges stay clean, on a slow one they drag a faint trail behind them. Here is what that means and what you can do about it.
Ghosting is a faint trail behind things that move on screen. It happens because the tiny dots that make up the picture cannot change color instantly — when they are slow, the previous frame lingers as a shadow of itself. A little of it is normal on most LCD screens; a lot of it makes games and scrolling look smeared.
Follow the moving blocks with your eyes — fullscreen works best, with nothing bright around the motion. On a healthy screen their edges stay reasonably crisp; ghosting shows up as a faded copy trailing behind each block, like a comet's tail. Try all three backgrounds — trails that are subtle on gray can be obvious on black, and the other way around, because pixels take different amounts of time depending on which shades they travel between.
If you see bright or oddly colored halos in front of or behind the blocks instead of a fading trail, that is overshoot — the monitor pushing its pixels so hard they fly past the target color before settling. The gray background is the best place to catch it: the blocks there are deliberately not fully white, so a halo brighter than the block itself stands out immediately. It usually means the overdrive setting is on its most aggressive level; turning it down one notch typically looks better than either extreme.
Most monitors have a setting that speeds the pixels up — usually called overdrive, response time, or trace free, and found in the monitor's own menu. Try the middle option first: the strongest setting often overshoots and trades trails for bright halos. On TVs, game mode switches off processing that adds smearing of its own.
Even on a perfect screen, an object you follow with your eyes looks slightly blurred — that is how displays that hold a still image between updates interact with human vision, and it is not a defect. The difference matters: a soft, even blur that is the same everywhere is normal, while a distinct trail or halo that clings to moving edges is the panel being slow.