UFO test
Track the moving craft with your eyes and compare the lanes. The blur you see on a normal monitor is mostly your eye smearing a held frame, not a slow panel.
Detected refresh: (browser estimate). Grey background is best for judging ghosting and overshoot; the checker helps spot judder.
What to look for
- Blur: the craft looks soft while you track it. This is persistence blur and shrinks as refresh rate rises.
- Trailing ghost: a faint copy behind the craft. The pixels are too slow to finish changing (response time). Try a higher overdrive setting.
- Bright or coloured halo: an outline lighter than the background behind the craft is inverse ghosting from too much overdrive. Step overdrive down one level. Our ghosting test makes this easier to judge.
- Stutter: jerky, uneven motion. Close other heavy tabs, or check the refresh rate test for dropped frames.
Why sample-and-hold blurs: try it
Blur width is roughly the distance the object moves during the time each frame is lit. Your eyes move smoothly, the image doesn't, so the frame smears across your retina. Change the numbers:
Perceived blur ≈ 6.7 px. 100% is ordinary sample-and-hold. Doubling the refresh halves the blur; so does lighting each frame for half the time (strobing).
This is the "persistence" model popularised by Blur Busters: 1 ms of persistence ≈ 1 px of blur per 1,000 px/s of motion. Pixel response time adds on top.
Questions people ask
What does the UFO test show?
It shows motion blur caused by how long each frame stays on screen (persistence), and any ghosting or trailing caused by slow pixel response. Follow the craft with your eyes: the faster lanes should look sharper.
Why is the moving UFO blurry even on a fast monitor?
On a normal sample-and-hold display each frame stays lit for the whole refresh. As your eyes track the moving object, the static image smears across your retina. At 960 px/s on 60 Hz, that smear is about 16 pixels wide. Higher refresh rates or backlight strobing (ULMB, DyAc, ELMB, BFI) reduce it.
What is the strobe option?
It inserts a black frame after every visible frame, a software version of black frame insertion. It halves the effective frame rate and brightness but shortens persistence, so tracking looks sharper. It flickers, so read the warning first; it works best at 120 Hz or higher.
Should I take a photo of the UFO test?
A normal photo won't show what your eyes see, because the blur happens when your eyes track the object. Reviewers use a pursuit camera that moves with the object to capture it.