How the LED Timing Matrix Works
The grid advances by exactly one cell every time your screen refreshes — 16.7 ms at 60 Hz, 8.3 ms at 120 Hz. If the screen misses a refresh, the grid skips a cell too, so it always stays aligned with real time. Beneath it, a 16-bit binary code shows the frame number in black and white squares, readable even after the grid wraps around.
Measuring Exposure Time
- Go fullscreen on the fastest display you have and frame the grid with the camera on a tripod.
- Set the shutter speed you want to verify and take a photo.
- Count the lit cells (include partly lit ones at either end).
- Exposure ≈ lit cells × display frame time. The calculator does the maths for your measured refresh rate.
Example: on a 60 Hz screen, two lit cells mean about 2 × 16.7 = 33 ms, i.e. roughly 1/30 s. The measurement is accurate to about one display frame, so it suits exposures longer than one refresh. Faster shutters light a single cell; use a 144 Hz or 240 Hz monitor for finer steps.
Checking Video Frame Rate and Dropped Frames
Record a few seconds of video and step through it frame by frame. If the lit cell advances by k cells per video frame, the camera’s frame interval is k × display frame time — 2 cells on a 60 Hz screen means 30 fps. An irregular jump reveals a dropped or duplicated frame, and the binary code tells you exactly which display frames were captured.
For slow-motion or high-frame-rate video, several consecutive video frames will show the same cell. Count how many frames each cell lasts: capture rate ≈ display refresh rate × frames per cell.
A Note on Rolling Shutter
With a rolling shutter, rows of the grid are captured at slightly different moments, so the lit cells may appear offset between grid rows. Count cells along the same grid row where possible, and see the rolling shutter test to measure the readout itself.
Shutter Speed Test FAQ
Why can’t I measure 1/1000 s with this test?
The grid changes once per screen refresh, so its time resolution is one display frame (16.7 ms at 60 Hz). Any exposure shorter than that lights a single cell. A faster monitor improves resolution, but very short shutter speeds need dedicated hardware testers.
What is the binary code under the grid for?
It encodes the frame counter as 16 black or white squares. Because the grid repeats every 60 to 120 frames, the code lets you identify the exact display frame in any photo or video frame, even across long recordings.
Can I check my phone’s slow-motion frame rate?
Yes. Film the grid in slow motion and step through the clip. Count how many video frames show the same lit cell; the capture rate is roughly the display refresh rate multiplied by that number.
Does the grid stay accurate if my computer drops a frame?
Yes. When a refresh is missed, the grid skips the corresponding cells so the lit cell always reflects elapsed time. The panel also logs every dropped frame in the last 30 seconds.