Isn't the sensitivity to flicker in the peripheral vision also related to
changing which receptors sense the light at the same time as the light is
turning on and off? For example, I find that I can often see the
multiplexing of LEDs if I just scan my eyes around their vicinity, as
opposed to trying to look straight at them or away from them.

On Fri, Oct 12, 2018 at 7:11 PM Harold Hallikainen <
harold@mai.hallikainen.org> wrote:

> Interesting! This reminds me of audio/video sync. We are very sensitive t=
o
> sound being early (before image), but very forgiving of sound being late
> (up to a point) since in real life, sound always arrives a little late.
>
> The two lights comparison is a little like "flicker fusion." In motion
> pictures, with a peak white screen illumination of 48 cd/M^2, we do not
> see the flicker with a flicker frequency of 48 Hz (two flashes per frame)=
..
> But, if the luminance is increased, we can see the flicker. The flicker
> fusion frequency increases with luminance.
>
> Another effect is we are more sensitive to flicker in our peripheral
> vision. I can see the flicker in a multiplexed LED display if I am not
> looking directly at it. If I look directly at it, the flicker is not
> visible. I understand this is an evolutionary development. Those of us
> (and other animals) that could see an attacker in the periphery survived.
> Those that did not did not.
>
> Perception is fascinating!
>
> Harold
>
>
>
> > I suppose many of us are familiar with the concept of "Nerd Sniping"?
> > https://xkcd.com/356/
> > "Nerd sniping is a slang term that describes a particularly interesting
> > problem that is presented to a nerd, often a physicist, tech geek or
> > mathematician. The nerd stops all activity to devote attention to solvi=
ng
> > the problem, often at his or her own peril."
> >
> > So, I was totally in the middle of something else, stopped, broke out a
> > breadboard and wrote code to answer this question....
> > At about 15mS, I cannot tell they are out of sync.
> > By about 20mS, I can see that it's not "right" but it's hard to say whi=
ch
> > is first.
> > At about 35mS, I can clearly see that they are out of sync and which on=
e
> > is
> > first.
> >
> > My results are likely skewed by having one red and the other green,
> though
> > I did flip them and try again with about the same results.
> >
> >
> > Code attached below.  Please note that I'm not claiming it's good
> code....
> > :-)
> >
> >
> >
> > void setup() {
> >   pinMode(D0, OUTPUT);
> >   pinMode(D1, OUTPUT);
> >   Serial.begin(115200);
> > }
> >
> >   int T1 ;
> >   int T2;
> >   int j;
> >
> >
> > void loop() {
> >   j=3DanalogRead(A0);
> >   T2 =3D j/10;
> >   T1 =3D 200 ;
> >   Serial.println(j);
> >
> >   digitalWrite(D0, HIGH);
> >   delay(T2);
> >   digitalWrite(D1, HIGH);
> >   delay(T1);
> >   digitalWrite(D0, LOW);
> >   delay(T2);
> >   digitalWrite(D1, LOW);
> >   delay(T1);
> > }
> >
> >
> >
> > On Fri, Oct 12, 2018 at 2:06 PM Gordon Williams <gwilliams@ncf.ca>
> wrote:
> >
> >> Hi,
> >>
> >> Hoping someone on the list may have some insight.
> >>
> >> I have 3 LED clocks that need to be synchronized for a nordic ski race=
..
> >> They show the time to the second.
> >>
> >> The way they are designed is they have a push button on the end that
> >> starts the timing.  The plan is to have a count down (3,2,1,go) with a
> >> person on each clock to push the button on "go".
> >>
> >> They will be synchronized close enough for timing purposes, but I want
> >> them visually synchronized as well so I don't get any complaints.
> >>
> >> Question: If the clocks are all in the centre of your field of view, h=
ow
> >> many milliseconds between the LED seconds digits changing can be
> >> detected? In other words, if you had 2 LEDs, what would be the maximum
> >> time difference between turning them on so you could say that LED A
> >> turned on before LED B?
> >>
> >> Thanks,
> >>
> >> Gordon Williams
> >>
> >>
> >> --
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>
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