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Putting an end to flickering LED's on mains Answered

Greetings everyone!

It's the time of year when colorful twinkling lights adorning nearly every structure you can see. LED's have become more popular as of late, and from an energy standpoint that's good. I know most people can't see a 60Hz flicker but I can, and it's quite unpleasant to sit across from a tree full of LED's all doing the same on-off-on-off nonsense.  I am fortunate to only get headaches though, other epileptics I've known have actually had AC LED's trigger seizures.

So what can be done about this? We bought LED strings before thinking about flicker and have since replaced them with incandescent ones, but I've still got all the LED strings in the closet. I'd really like to be able to use them.  Perhaps I could fashion a device that acted as a middleman between the outlet and the plug on the lights that would smooth the incoming current?

I have two ideas for this: 

1.  Filter incoming current with an RC circuit
2.  Rectify the mains voltage

I'm curious if anyone else has attempted, solved, or even just noticed this frequency problem? I don't mind re-inventing the wheel, but I'd rather not build it square.

Happy holidays! **yes, I just said happy holidays. Deal with it. :)


you could try a power supply that will increase the frequency, making the flickers less visible and that will avoid the need for rewiring anything.

I can't really follow you here unless you are talking about LED strings that are powered directly by mains voltage.
Usually LED strings work at low voltage levels and if there is a flicker visible for you there could be two reasons:
a) The LED string is connected to a "dimmer" or other effect device (some strings come directly with one.
b) The LED string uses a very cheap and bad power supply.
Both problems can be solved with a filtered DC voltage to feed the LED's although the dimmer would need to be replaced or abandoned if it causes the flicker.

Hello! Yes, the lights I'm talking about are directly powered by AC (LED Christmas tree lights that have no DC driver incorporated. A dimmer may allow me to minimize obvious flickering, but seems like would do so by just not getting as bright...So less of a change when the lights turn on and off at 60Hz. Thanks for your ideas though, I'd not considered a dimmer.

Unfortunately, it's possible that an LED-compatible dimmer would make your "observable flicker" problem worse, not better. LEDs don't illuminate unless the applied voltage is above threshold, so a normal dimmer (which just reduces the voltage, and hence the current, across a resistive load) will just turn them off.

Instead, LED dimmers work via "pulse width modulation," which turns the current off and on very rapidly, so that the blurred together on-and-off states appear to be a continuous, but dimmer, light.

Downunder is quite rude for not having a good understanding here. yes led xmas lights are powered directly off main AC power.

try powering the leds from 120V DC instead of DC. The world war Two liberty ship Jeremiah O'brain was built with a 120DC power system. The people maintaining it found 129VAC compact flourescent lamps work fine in 120VDC I don't know if it would work becasue it would depnd on how the light string is wired.

Did you make a typo or just fail to understand electricty?
Just wondering as DC is DC no matter the voltage.
And rectifiers were already suggested.

you are rude and are the apparent one who doesn't understand electricity... when did Steven say DC is not DC????

This is a problem that I, too, notice. I've been meaning to fix this. Bridge rectifier + capacitor might do it.

AC powered led strings without a proper driver?


Well, since I bet your strings don't follow the aforementioned article's theory of operation, do you mean dual reverse polarity coupled and resistor ballasted led strings?

If you can un-couple the strings, you could drive them with a high output voltage AC led driver, as long as the driver's output current fits the bill, of course. For less than $7 I know of an online store where you can get a 300mA buck/boost one able to deliver up to around 120V (tested to 150V) to the load, consequently it could drive these strings even without bridging the ballast resistors (I'd bridge them). An adecuate number of strings would have to be set in parallel to match or exceed the driver's current output (4 × 100mA strings, for example). Leds are plentifully bright even if driven way below their maximum ratings, as they operate hyper-efficiently in such cases.



2 years ago

Ideas 1 + 2 have a name: a mains-fed DC power supply. ;-)

Certainly you can do this, for "dumb" LEDs. You've gotten some good input. I'll add one more consideration--rectifying and filtering AC (to convert to DC) yields a higher voltage than the AC. With solid state diodes / rectifier, the voltage gain is about 1.4 times the AC RMS voltage.

The filter caps in your power supply store voltage up to the AC peak, which is higher than the AC RMS (a "mean" metric, or an average). When your LEDs were wired directly to the AC, an average voltage was applied. With DC, it's the peak voltage constantly. Be sure to take that higher voltage into account.

BTW, directly-rectified mains voltage is generally frowned on, safety-wise.

The problem comes from the fact that LED are themselves diodes and only lets electricity go through them one way. When traditional bulbs light up, the alternating current from the main pulses 60 times a second in each directions but LED's only pulse in one direction. So they only get half as many pulses and it is like they are operating at half the frequency. So the blinking is more noticeable.

The simplest solution use a square bridge rectifier.


This switches all the pulses to going in the same directions so that it is again blinking at the same frequency as traditional bulbs. The problem with this is that most LED strings have multiple sections that are in alternative orientations so that they don't all light up at the same time. So with a square bridge rectifier some of the lights won't turn on. To fix this, you would have to cut out the section that won't light up and turn this section around.

Another option is to take two strings of lights and connect them end to end, then fold them in half so that the first light on one string lines up with the last string on the other. If you position these two lights right next to each other, the blinking will be less noticeable because the two lights will be blinking alternatingly.

A bridge rectifier was exactly what I was thinking, and definitely among the easier mods to make. To address the 'reversed' portions of the strings I suppose that a DMM would do the trick to help me determine where these sections are (which I'd never heard of, but makes perfect sense though).

Thanks a bunch for your input. I'll try to post results after I make it through the upcoming festivities.

Do you have a link or pic of the string by any chance?
Was wondering if it is clear how they are wired internally to get them working on a clean DC.
Normal strips just have a single resitor per section to get current limiting done.
This gives 2 connections for the power.
Some mains LED strips have 4 connections others just 2 and the stuff to get down to a usuable voltage is on the strip itself.