# Preventing LED micro flicker

I know there are many questions floating about "howwant to drive a LED" going around (and many many good answers), but please bear with me.

The concern is how to make sure that my LED's don't have any sort of flickering, not even "micro-flickering" that's undetected by the human eye, as that can have health effects on both humans and plants (here are a couple of anlisys: https://www.digikey.com/en/articles/techzone/2012/jul/characterizing-and-minimizing-led-flicker-in-lighting-applications, https://www.azom.com/article.aspx?ArticleID=12161).

As I understand, LED micro-flicker may come from 3 sources:

1. Noise carried over from the AC line
2. Noise carried over from up-regulation of the AC frequency (present even in most high-frequency switching power supplies)
3. Flicker introduced by PWM for dimming

Here is my current prototype which should eat up about 72W if my math is right. I'm calculating the "ideal" Vf for each LED based on meassurements for the min and max Vf and max If, procuring the voltage never causes the current to exceed 76% of the max If. All the data of the components in link is according to reality.

I'm using the 12v rail of a PC PSU, because I thought "hey, this thing's used for powering micro-processors, it's gotta get rid of 1 and 2, right?" (though I haven't assertained that with an oscilloscope yet).

I'm guessing eventually I'll use a commercial 12v switching power (unless I realize that they all have problem number 2).

As for why I care about problem number 3, well, I'd very much like the lamps to be dimmable, quite possible controlling the diming from a micro-controller which (I hope) would be able to take the LEDs from fully-off (ie, just below the Vf) to fully-on (zero resistance, besides what I've put before each series).

Are there better ways to get a stable noise-free powerline? or to regulate the current programmatically without using a PWM?

Q: What is an efficient and cost-effective way to drive and regulate brightness for high-power LEDs ensuring a light output that's free of micro-flicker and as free of noise as possible?

• From an engineering persprctive: there is no such thing as "noise-free". There is only hunting for and reducing noise sources. But there needs to be a reasonable, cost-effective threshold of acceptable noise, otherwise there really is no solution. You've rejected human-eye-detectable flicker as not good enough, yet seem to want 0 noise at room temperature. Using the crummy 12VDC from a computer offline switcher is inconsistent with your stated goal. Batteries would be the best bet for low noise, but there's still going to be some ambient noise from the power grid. What's the real goal? Apr 17, 2018 at 22:33
• That "site" is questionable and by questionable I mean bad science. By the way regular lamps switch on and of 60 times a second, and we've been using those for a hundred years. They also experience flickering as they are tied directly to the grid. If you want to make money, then scare people and charge them, it also helps to have a Phd next to your name Apr 17, 2018 at 22:51
• 'Flickering' is due to poor/cheap designs, or use of a conventional light dimmer on LED's. A proper LED driver/dimmer will pulse much too fast to have any flicker.
– user105652
Apr 17, 2018 at 23:28
• I'm sorry if this comes off as condescending and dismissive, but do you know how computer monitor/ phone display works? Having a hard time approaching this answer seriously while reading it through several hundred thousand flickering light sources. Apr 18, 2018 at 3:18
• @laptop2d "By the way regular lamps switch on and of 60 times a second, and we've been using those for a hundred years." - I agree with the gist of your answer but that statement isn't very accurate. Incandescents have a lot of thermal inertia so while current through them falls to zero 100 or 120 times per second (not 60!) and they do flicker at that frequency, their light output varies only by some 10-20% or so, nowhere near on/off flicker that LEDs might exhibit. Apr 18, 2018 at 15:10