GUIDE 05 / 07
How Monitor Refresh Rate and Screen Size Affect Dynamic Vision Measurement
On a 60 Hz screen, a fast target skips between frames and looks blurred to a tracking eye. We explain how refresh rate, screen width, and brightness change results, with worked examples.
Motion on a screen isn't continuous — it's a still image being swapped out rapidly. That means dynamic vision measured on a screen is shaped not just by the human eye but by the screen's own properties. That's why this site shows refresh rate, distance moved per frame, and exposure time alongside your result.
Distance moved per frame
At a 60 Hz refresh rate, the screen redraws 60 times per second. If a target moves at v px/s, it jumps v ÷ 60 px each frame.
Move per frame (px) = Speed (px/s) ÷ Refresh rate (Hz)
| Speed | 60 Hz | 120 Hz | 144 Hz | 240 Hz |
|---|---|---|---|---|
| 600 px/s | 10 px | 5 px | 4.2 px | 2.5 px |
| 1,200 px/s | 20 px | 10 px | 8.3 px | 5 px |
| 2,400 px/s | 40 px | 20 px | 16.7 px | 10 px |
| 4,800 px/s | 80 px | 40 px | 33.3 px | 20 px |
This site's DVA target is 44 px in diameter. At 60 Hz, once speed exceeds about 2,640 px/s, the target jumps farther than its own size each frame, and it may look like a series of stamped dots rather than motion. The result screen flags this case separately.
Blur in a tracking eye
LCD and OLED screens typically use a sample-and-hold method, keeping the same image displayed for the whole frame. While your eye smoothly tracks the target, the target on screen stays in place for the entire frame, so on the retina it appears blurred by roughly the distance moved per frame. At 1,200 px/s on a 60 Hz screen, this creates nearly 20 px of blur, making a ring with an 8.8 px gap hard to identify. A higher refresh rate reduces this blur, making the same speed easier to see.
How is refresh rate measured
The browser calls a requestAnimationFrame callback every time it redraws the screen. This site measures the callback interval over about 120 frames and estimates the refresh rate from the median; if it's close to a standard value like 60, 75, 120, 144, 165, or 240 Hz, it displays that value. If the interval is uneven, a ? is shown next to the value.
- Low-power mode on laptops and phones can lower the refresh rate to 60 Hz or below.
- Variable refresh rate screens (like ProMotion) change their refresh rate depending on the situation. Try re-measuring with the ↻ button right before your test.
- When a browser tab goes to the background, drawing stops, so the measurement is voided.
Screen size and exposure time
Even at the same px/s, a narrower screen gives a target less time to cross it. Crossing a 1,000 px wide area at 2,000 px/s takes about 0.5 seconds, while on a 400 px wide phone it takes about 0.24 seconds. Shorter exposure time makes reading harder, so don't compare px/s scores across different devices. Calibrated °/s reduces some of the difference between devices, but doesn't eliminate the difference in exposure time.
Brightness and contrast
Brightness has a big effect on results — enough that one study found the decline in dynamic vision among older adults nearly disappeared when the optotype's brightness was raised (Long and Crambert, 1990). Keep track of your screen brightness, room lighting, and whether dark mode is on, and test under the same conditions.
A checklist for a fair measurement
- Same device, same browser, same window size
- Same viewing distance (entered in the calibration panel)
- Same screen brightness and theme
- Confirm the displayed refresh rate matches your usual setup
- Test multiple times and look at the average value rather than your single best score