eye's response

[cadstarsucks]

found a good reference for the eye's light response:

http://webvision.med.utah.edu/index.html

Dan

[kinnza]

Wow! Thank you very much for that link, Dan, ive been long time trying to find such complete info. 

[cadstarsucks]

Wow! Thank you very much for that link, Dan, ive been long time trying to find such complete info. 

You're welcome... I found it on one of my "trips" in search of solid statements supporting mux'ed brightness/efficiency claims.  I never doubted it, since it came from electronic houses in app notes about LEDs, but it seemed as though I was catching flack about the statements.

Dan

[kinnza]

Yep, that the same as me. Ive been long time trying to find solid scientific knowledge about how the human eye measure light, brightness and color.

Specifically, i want to how much imperfect is our eye averaging PWM pulses. Many leds designers says PWM induces higher brightness feeling than the averaged brightness, while other says the human eye is a perfect integrator (overall perceived brightness is same than the averaged emited brightness).

I asked this question at the psyciphysic group at Google, but the only thing clear is that our eye is an imperfect integrator, but it seems the the degree of desviation in the integration process depends of some different factors (frecuency of PWM, wavelenght, brightness of the max pulse...), so ive been unable to find a way of calculating how much enhancement of perceived brightness PWM induces (compared to the physical averaged emission). It can be of 3% or 20%, no idea.

Ive been reading this page carefully, and they dont clarify this question, although is great for colorimetry concepts. Im thinking to ask directly to the authors.

[abnormal]

Cool find Dan!  Thanks!

That's more than a 5 min. read! 

[cadstarsucks]

I asked this question at the psyciphysic group at Google, but the only thing clear is that our eye is an imperfect integrator, but it seems the the degree of desviation in the integration process depends of some different factors (frecuency of PWM, wavelenght, brightness of the max pulse...), so ive been unable to find a way of calculating how much enhancement of perceived brightness PWM induces (compared to the physical averaged emission). It can be of 3% or 20%, no idea.

Ive been reading this page carefully, and they dont clarify this question, although is great for colorimetry concepts. Im thinking to ask directly to the authors.

The section of interest is: http://webvision.med.utah.edu/temporal.html

And the one graph that seems to make sense of it is: http://webvision.med.utah.edu/imageswv/KallTemp6.jpg

Notice the huge peak for short, high power pulses.  I would have liked to see a couple more higher power entries in that graph.  Following the trend leads one to believe the perceived intensity doubles for every 50 lux and you then you can approach triple if you further reduce the pulse width.

Dan

[BVnursery]

My wandering thru spec sheets has led me to believe that led output tends to significantly flatten off at about 2.5x their rated power.

For my area of application,  sorta be a waste even with a PWM to exceed that.

[cadstarsucks]

My wandering thru spec sheets has led me to believe that led output tends to significantly flatten off at about 2.5x their rated power.

For my area of application,  sorta be a waste even with a PWM to exceed that.

Actually BV, PWMing would not help at all since the increase is in the perception not in the actual power. 

Your grow lamps need actual luminous flux barring a similar characteristic in plants.

Dan