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Dim an LED, how does it react?

SimonTHK

Member
A smaller quistion.
I have tried to dim an LED, but it seems that I cant see the effect, before it reaches a small amount of turned on time, like 20%. Can this be true?
I use a PWM signal.

Best regards Simon
 

Diver300

Well-Known Member
Most Helpful Member
Eyes are not good at seeing absolute brightness. It doesn't surprise me that you have to turn down to 20% before you see a difference.

When cameras had shutter speeds and F-stops, I measured how much light difference there is between outside in full sun inside a building with normal size windows. The difference was 1000 times. Of course it seemed darker inside but it really didn't seem that different.
 

SimonTHK

Member
Ok so myabe it makes sense. That I turn it down in 30 steps from 100%. 3% turned on per time. So maybe only few steps is visible to the eye.
Thanks
 

SimonTHK

Member
so I went from 300 hz to 15000 hz. I didnt change the duty cycle, but it did change the brightness of the LED. Simply it isnt on for so long at a time, but still am on for the same percentage of time.
Apparently this can make a difference aswell! I guess.
 

SimonTHK

Member
I Dont know what to conclude from this. Other than that I should probably use quite high frequenzy HZ while doing this.
 

gophert

Well-Known Member
Most Helpful Member
.
 

audioguru

Well-Known Member
Most Helpful Member
Without changing the setting of the iris in each eye that adjusts your sensitivity to light, you can see an extremely wide range of brightness from moon-light to sunlight so the sensitivity is logarithmic, not linear. Our sensitivity to loudness is also logarithmic so a volume control is logarithmic.
You need logarithmic control of the PWM.
 

Pommie

Well-Known Member
Most Helpful Member
Assuming Arduino and only 256 PWM steps then only 6(7) levels available. 255,93,34,12,4,1 and zero of course. Do these values look like linear steps in brightness?

Mike.
 

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