In this question, user @glen_geek posited (with linked references) that perceived light from an LED versus actual light from an LED is greater at lower duty cycles:

@kando For PWMing LEDs, people.csail.mit.edu/jstraub/blog/How-to-dim-a-LED-for-humans suggests that half-brightness occurs at about 8% PWM in the 2nd-to-last graph.

For perceived brightness non-linearity, you might try: pathwaylighting.com/products/downloads/brochure/…

Possible Clarification

I assume that the plot of specific constant duty cycles (in 100 [ms] periods):

Specific Constant Duty Cycles

is not correlated to the figures of the dynamic cycling duty cycle (in 200 [ms] periods), as this would require the actual duty cycle period to be order(s) of magnitude smaller to achieve any precision in the dynamic duty cycle being discussed:

Duty Cycles : Linear

Duty Cycles : Exponential


If the eye amplifies light for smaller PWM duty cycles at cycle frequencies which are much greater than the perceptible flicker rate (>>200 [Hz]), could an LED be made more efficient (in terms of perceived intensity vs input power) by only operating at lower PWM duty cycles?

  • 2
    \$\begingroup\$ Why not download the papers? You will want at least these: Talbot-Plateau law, Weber-Fechner law, and also the related Broca-Sulzer effect and the Bruecke-Bartley effect. At a minimum. Those go back to when I cared. I'm sure there's much more in the literature, today. I have those somewhere here, by the way. (And a book on the topic, though I've since forgotten the title and my wife has had me packing books into boxes.) Engineers, I think, should have a simple summary page for times when they may care -- which apparently isn't very often. \$\endgroup\$ Commented Jun 12, 2023 at 20:49
  • \$\begingroup\$ @periblepsis : Interested in a new topic? That's a citation. Confusion on said topic? That's another citation. (I love a good reference to uhh.. a good cited reference.) Thank you for the keywords. \$\endgroup\$
    – kando
    Commented Jun 12, 2023 at 20:55
  • 2
    \$\begingroup\$ There's a subtle difference you may need to grab up. The Talbot-Plateau law suggests, for example, that operating light at 50% duty (above the CFF) will appear as the same brightness as another operating at half the luminence and at 100%. Note that this is not the same thing as saying that it will appear half as bright as one operated 100%! This other case is where the Weber-Fechner law comes in and says that intensity goes as the logarithm of the physical stimuli. Human perception of brightness must follow the log, as we need to see over many orders of illumination. \$\endgroup\$ Commented Jun 12, 2023 at 21:02
  • 2
    \$\begingroup\$ There are also differences between cones and rods. In the cones, brightness is only perceived using one of the color pigments. Not all three pigments. This also means that evolution strongly opposed mutations that would "break" that particular pigment. But the other two pigments are allowed to be more variably mutated. The peak wavelength of sensitivity is different between scotopic and photopic vision, as well. Side note: women perceive finer color gradiations than men. Never knew a man who could pass a color test used for photo color checker jobs, for example. \$\endgroup\$ Commented Jun 12, 2023 at 21:05
  • 2
    \$\begingroup\$ @kando I spent some years in a certain sub-specialty in this general area of human color and brightness perception. Note that mutation rates are controlled, at least in part, by the number of hydrogen bonds related to combinations of the four base pairs found in DNA. For example, there are 5 of 20 amino acid residues, Asn, Gln, Asp, Glu and Arg, able to orient in a coplanar fashion in order to form pseudo pairs with nucleotide bases through two hydrogen bonds. This reduces the likelihood of mutation. \$\endgroup\$ Commented Jun 12, 2023 at 21:15


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.