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Suppose I have a line of N LED's, of which only one is on at a time. Is there a formula relating N to the minimum speed at which I have to switch between one being on and the next one?

IE: I give the formula my number of LEDs and then out comes the frequency at which I must cycle through them.

NOTE:

This should work in such a way that a human can not distinguish that any of the leds where off

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  • \$\begingroup\$ Other than FPS*N? \$\endgroup\$ Commented May 21, 2016 at 16:28
  • \$\begingroup\$ Do you need the transition from one LED on to the next to be indistinguishable to the human eye with the LEDs apparently moving (no time when they are both off as far as the observer is concerned)? \$\endgroup\$ Commented May 21, 2016 at 16:30
  • \$\begingroup\$ @PeterSmith Yes \$\endgroup\$ Commented May 21, 2016 at 16:35

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Going back to the old video standards (such as PAL or RS-170), the refresh rate was 25 frames per second or 30 frames per second (depending on where you live).

The refresh rate was chosen to be as low as possible (to keep the electronics reasonably inexpensive and achievable) but high enough so that the viewer did not suffer distracting (and possibly to some) painful flicker sensations.

These standards were interlaced, so 20msec between one device turning off and the next turning on should work.

In what I currently do, we consider that 5 msec is not resolveable by the human eye. That basis should let you answer your question.

As an example of where we deliberately flicker an LED but it gives an appearance of continuous operation, see this previous question.

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    \$\begingroup\$ There were two further tricks to the TV. (1) The phosphor coating inside the tubes had a decay time. This had to be slow enough to keep the dot bright for a while but not so long as to blur the image. (2) The 625 lines of scan were interlaced with, I think, all the odd lines drawn first followed by the even. This way every pair of lines had one of them refreshed 50 times a second. \$\endgroup\$ Commented May 21, 2016 at 17:14

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