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Human Eye -- Peak or Average Response

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David Hess:

--- Quote from: wraper on June 08, 2019, 11:58:21 am ---
--- Quote from: David Hess on June 08, 2019, 03:05:25 am ---
--- Quote from: wraper on June 08, 2019, 01:53:51 am ---PWMed one should have lower brightness due to LEDs having lower efficiency at high currents.
--- End quote ---

This depends on the LED.  High brightness LEDs can have lower efficiency below 100s of milliamps which is one of the advantages of multiplexed operation.
--- End quote ---

If LED can work at 100s of milliamps (even peak), and especially have high efficiency at that current, it's high power LED, not simply high brightness LED.
--- End quote ---

I am not going to waste time finding a specific example to refute that.  My point is that it can be more efficient to multiplex (or PWM) an LED at higher current than to drive it at a continuous lower current.  This depends on the specific LED characteristics.

The high brightness AlGaAs red LED for displays shown below is more efficient if multiplexed at 10 milliamps instead of being driven at 1 milliamp or lower for the same brightness.  Some (newer) LEDs have a very linear intensity curve at low currents so this does not apply to them.

wraper:

--- Quote from: David Hess on June 08, 2019, 06:58:00 pm ---The high brightness AlGaAs red LED for displays shown below is more efficient if multiplexed at 10 milliamps instead of being driven at 1 milliamp or lower for the same brightness.  Some (newer) LEDs have a very linear intensity curve at low currents so this does not apply to them.

--- End quote ---
See the difference between 10mA and 100s of mA? PWMing is certainly not a way to achieve high LED efficiency. You would need to drive powerful and expensive LEDs at fraction of their rated current where efficiency peaks and then reduce power even further by PWM.

--- Quote ---My point is that it can be more efficient to multiplex (or PWM) an LED at higher current than to drive it at a continuous lower current.
--- End quote ---
Only if you use them at small fraction of rated power when PWMed compared with tiny fraction at constant current. You would be much better by just selecting weaker LED.

Zero999:

--- Quote from: wraper on June 08, 2019, 07:43:35 pm ---
--- Quote from: David Hess on June 08, 2019, 06:58:00 pm ---The high brightness AlGaAs red LED for displays shown below is more efficient if multiplexed at 10 milliamps instead of being driven at 1 milliamp or lower for the same brightness.  Some (newer) LEDs have a very linear intensity curve at low currents so this does not apply to them.

--- End quote ---
See the difference between 10mA and 100s of mA? PWMing is certainly not a way to achieve high LED efficiency. You would need to drive powerful and expensive LEDs at fraction of their rated current where efficiency peaks and then reduce power even further by PWM.

--- End quote ---
Some LED types also exhibit a shift to shorter wavelengths, as higher currents. Some of the high brightness green LEDs appear almost cyan when overdriven. The human eye is also less sensitive to shorter wavelengths, than green, especially at high intensities, so efficiency will drop more.

Someone:

--- Quote from: jweir43 on June 08, 2019, 05:43:27 pm ---Could you possibly translate that into a yes or a no instead of a maybe?

THanks,

Jim

--- End quote ---
Perhaps you would like to pay a professional for a report on the matter? Expecting an exact answer for free seems a bit presumptuous.

jweir43:
Don't know why?  I'm a pro at what I do, but I certainly share my knowledge when asked.

Jim

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