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Is this LED current ripple going to be visible as flicker?

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treez

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The LED curent is as in the attached.
I cannot see this ripple, but some people can?
(its at 100Hz and it is the output of a PFC'd flyback led driver)
 

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Thanks, but this flicker is how its supposed to be , because i do not have big capacitor on dc bus because it is pfc'd flyback......it is led current flicker.
Also, i do not have big secondary electrolytic cap as i dont want wet electrolytics...so i suffer the led current ripple happily...as long as nobody can see it....but can they see it?

Also, the attached flicker below is 120hz led current ....when the same pfc'd flyback has a triac dimming it up front....would this led current result in visible flicker.?...i cant see the flicker but maybe others can?
 

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Looks like this is a slippery theme. Did you see this article?
You should distinguish requirements for LED flicker and personal perception (every man to his own taste).
You can arrange your own quiz and ask all your acquaintances can they see flicker or not. You can find out about requirements for LED flicker and to make compliant system. However standard compliance won't garantee that no one can see flicker. You can try to improove your schematic or choose another. It's all up to you.
 

Hi,

Visible or not?
It depends:
* on the person
* on the size of the light source
* on ambient light
* on movement

There is a good chance that someone recognizes it.

I have a 240Hz LED driver, PWM, hard ON/OFF.
On a small LED source I can see it when I move my eyes. It is not very annoying, but visible to me.
But it's not visible to me with LED panels, or without movement..

Klaus
 

Interesting question. I measured the light output of a few retrofit LED bulbs and found different amount of 100 Hz ripple, mostly below 20 percent. A chinese corncob lamp showed 100 percent modulation, similar tow 50 Hz ballast fluorescent lamps.

I don't perceive 100 Hz ripple of fluorescent lamps, and I didn't yet meet someone who does. That you can see it when moving your eyes fastly is a different thing.

Unconscious physiological effects of 100 Hz ripple have been however reported. I wonder if there are any quality standards referring to light ripple?
 

Obviously, each person has their own depth of perception when it comes to light level variations. You can't really compare fluorescent lamps with LEDs either because the phosphor in FL/CFL tends to have a slower decay rate than the stuff used in LEDS.

I have an application where a bank of 20 high power blue LEDS (~2A when on) are chopped with a PWM signal at 1KHz to dim them and it looks perfect viewed face on but still has very noticable flicker if the viewer or their eyes moves quickly. This application is for underwater lighting and the diffraction from waves on the surface makes them look very 'dotted'. In hindsight I would have designed it to work at higher frequency.

Brian.
 

thanks, i think the duty cycle of the pwm dimming has an effect too.....for example, if the duty was 0.75 then the flicker would likely not be seen (?). If 0.05, then it would probably be visible flicker, even at your 1khz
 

You can't really compare fluorescent lamps with LEDs either because the phosphor in FL/CFL tends to have a slower decay rate than the stuff used in LEDS.
Click to expand...
You can well compare it related to 100/120 Hz ripple. Phosphor decay time constant filters part of the high frequent switch mode ballast ripple but effectively no 100/120 Hz choke ballast ripple. Just try.

Operate a photo diode in photovoltaic mode. Assure linear V/I response by adjusting the load resistor to give not more than 100 to 200 mV output, connect an oscilloscope.

In a static illumination situation, you perceive the ripple filtered by the low pass characteristic of your eyes. Duty cycle doesn't count in this relation, just ratio of ripple fundamental wave magnitude to average intensity. In moved eyes or moved object scenarios, low duty cycle can indeed increase the ripple perception.
 

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