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I'm setting up one of my first circuits. I have a knob to increase the flickering speed of a led. When I increase the flickering speed up to a certain point I am not able anymore to perceive it is flickering. When I increase the flickering speed even more the led dims.

Why? Some sort of wave interference effect?

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Educated guess:

The LED can't turn on and off instantaneously so your LED isn't operating as a perfect square-wave. There is some curvature at the edges. When you flicker too fast, the LED can't turn itself on fast enough.

Example with numbers: Say it takes 1 ms for the LED to go from dark to light or vice-versa. If you're telling it to flicker with a period (off to on to off) of 1 ms, your LED will never reach peak brightness. It will look more like a series of hills. As you flicker even faster, the hills will shrink further.

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  • $\begingroup$ Makes sense to me. $\endgroup$ – Bentley4 Aug 14 '13 at 21:26
  • $\begingroup$ 1 ms to start electroluminescence looks way too long. Normally a diode fully opens in several ns to tens of ns, and luminescence starts immediately proportional to current (if we ignore temperature dependence). $\endgroup$ – Ruslan Aug 15 '13 at 20:29
  • $\begingroup$ As another commenter mentioned, there is likely some inductance, which can slow things down considerably. $\endgroup$ – AlexQueue Aug 21 '13 at 14:42
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Human eye takes 24 frame per second, approximately 70GB data. If you blink LED above some frequency, you may not see the off state of LED. You see LED is on continuously. For more info: Persistence of vision. But high speed cameras capture it, it actually blinks. There are some videos on youtube. There is a method called LED matrix which takes advantage of this. LEDs are turned on and off at high speed and user see all of them on. This method requires less control pin and gives expected result. Why we see it dimmed instead of on or off states? I think it's also sensitivity of human eye. You may not see darkness right after the lightness. Luminosity function. Power consumption of blinking system with clock (square wave) is almost half of the power consumption system with stable signal. But when you increase frequency, you see the LED more bright. And I think, lifetime of LED may be doubled because of use time...

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  • $\begingroup$ Where did you get that 70GB data figure? could you provide a reference. $\endgroup$ – udiboy1209 Aug 15 '13 at 10:04
  • $\begingroup$ From a documentary I've watched. But I don't remember the name.. Sorry. Should I delete? $\endgroup$ – Onur Aug 15 '13 at 19:47
  • $\begingroup$ It's not a reference, but when I searched, a youtube link appeared, and someone has comment (hassi44 2 months ago) which says similar things. Probably watched same documentary or there is some info on somewhere. youtube.com/watch?v=PBfKbOEWR6I $\endgroup$ – Onur Aug 15 '13 at 20:05
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    $\begingroup$ International Journal of Communication 6 (2012), 907–919 1932–8036/20120907 One in a Million: Information vs. Attention MICHAEL LESK Rutgers University ijoc.org/index.php/ijoc/article/viewFile/1567/739 Page 912 "The total bitrate into the eye would thus be over 25 GB/second. How much does the eye reduce this as it sends signals to the brain? Koch et al) (2009) suggest that about 10 million bits per second, or about 1 MB/s, move from the retina to the brain." My fault was: eye receives GBs of data, but sends MBs of data. I will edit my text. $\endgroup$ – Onur Aug 15 '13 at 20:19
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This is the result of simple averaging.

At low rates you eye separately measures and reports the intensity during the bright period and the intensity during the dark period. When the rate exceeds the response time of the eye, the report is effectively the average brightness which is necessarily less than the brightness of the bright periods.

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