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Hero999 said:PWM is only useful when dim the LED or use an LED that's most efficient when pulsed at a high current at a low duty cycle, if your LED is most efficient at the normal continious current rating then PWM is a waste of time.
cadstarsucks said:That is not accurate. The human eye acts as a differentiator and an integrator. That means that that it detects an intensity peak and then drifts down.
The end result is that even though the optical power is lower, the apparent intensity can be higher.
D.
frenzee said:That is incorrect. The human eye sees the avaerage brightness, not the peak brightness:
https://members.misty.com/don/ledp.html
Still, pulsing an LED at twice the rated current at half the dutycycle will still look as bright as an LED run continuously at the rated current. The power dissipation in the resistor will be exactly the same so you've gained absolutely nothing in efficiency. The only time you will gain is if the LED is more effiecient at higer currents but this only applies to some red and inrfared LEDs, you loose with blue and white LEDs because they're more efficient at low currents and the PWM circuitary uses power.cadstarsucks said:I did not say it sees peak... I said it registers a peak and then drifts down. the apparent brightness is the average of the result.
cadstarsucks said:I did not say it sees peak... I said it registers a peak and then drifts down. the apparent brightness is the average of the result.
I can't find a REAL source off hand so I will have to rely on Maxim blech!
**broken link removed**
"An advantage of pulse drive is that the human eye behaves as a partially integrating and partially peak-reading photometer. As a result, the eye perceives rapidly pulsed light somewhere between the peak and the average brightness. This means that a low-duty-cycle, high-intensity pulse of light looks brighter than a DC signal equal to the average of the pulsed signal. An advantage of multiplexed operation, therefore, is an improvement in display intensity for a given average power consumption."
D.