LED Christmas Lights PWM?

markr6 · Nov 26, 2013

I don'tknow why they would have PWM, but it seems similar to me. If not, why do all LED Christmas light sets seem to flicker?

I bought a string of 100 white lights to try out for $6.99. I took them back to stick with the good old incandescents. The flicker was driving me crazy. Mostly when you move your eyes around or while walking. I notice this on everyone's house with LEDs as I drive around. Maybe it's just me but I even have a hard time focusing on the colored LEDs, especially blue at night. Almost like I have depth perception.

AnAppleSnail · Nov 26, 2013

This is why I don't buy cheap LED Christmas lights that plug into the wall. They run on (usually) unrectified AC, so in the US they flicker at 60Hz, or in Europe at 50Hz. During the 'positive' part of the AC wave, they are on. During the negative part, they are off.

If the manufacturer added a rectifying bridge (Coupla cents of diodes) would make them flicker at twice that frequency, but 120/100Hz is still quite visible. I can really only stomach DC-powered Christmas LEDs.

Changchung · Nov 26, 2013

For that price this dont bother me... hahhaa I have a few installed already...

markr6 · Nov 26, 2013

I picked up 12 sets of incandescents for next to nothing. So about $.05/hour total, 5hrs each day for about 40 days = $10 extra on the power bill for the year. Good enough for nice looking lights I guess.

On a side note, I know of some people that just rip them off their shrubs/trees and throw them out each year. I guess $2 isn't worth the hassle of keeping them. Seems wasteful but that's their choice.

EngrPaul · Nov 27, 2013

PWM = Pulse width modulation, used to control the power delivered to the LED's.

Unless the lights have a dimming circuit, you are likely noting directly rectified AC power, not PWM.

Mine do this. I don't care, as long as they are warm white and outdoors.

StarHalo · Nov 27, 2013

I prefer PWM in Christmas lights, it really draws the eye. I'd slow the rate down to 30hz or so if I could just to make them stand out more.

jtr1962 · Nov 27, 2013

It's not terribly expensive to make LED Christmas lights which don't flicker. For example, the circuit below which I used to mod a nightlight with LEDs will also run a string of 25 Christmas lights without flicker. In fact, you could even drop the size of the filter cap C2 by an order of magnitude and still not have much modulation in light intensity. The parts here cost pennies. Certainly most people are willing to pay ten cents more to have lights which don't flicker.

subwoofer · Nov 27, 2013

markr6 said:
I don'tknow why they would have PWM, but it seems similar to me. If not, why do all LED Christmas light sets seem to flicker?

I bought a string of 100 white lights to try out for $6.99. I took them back to stick with the good old incandescents. The flicker was driving me crazy. Mostly when you move your eyes around or while walking. I notice this on everyone's house with LEDs as I drive around. Maybe it's just me but I even have a hard time focusing on the colored LEDs, especially blue at night. Almost like I have depth perception.

This is very prevalent, even in the ones put up by the local council as street decorations. I dislike PWM wherever it may be. And having seen it in even quite expensive LED Christmas lights, have stuck to incans.

I agree with blue LED lights at night and having difficulty focusing. This will be due to the blue light being a very specific wavelength (near the limits of our vision) and when your eyes are adjusted to low light, your pupils are wide open making the different focal length of your eye's lens for different wavelengths of light more obvious (similar to a wide aperture and short depth of field in photography).

I wish manufacturers would spend just a little more time and a tiny bit more money on making lights PWM free. People really are starting to see the quality of light getting worse as LEDs are used more. I still can't find 'warm' enough LED bulbs for home use, but that is another topic for discussion.

markr6 · Dec 9, 2014

A year later...still using about 10 sets of incandescent string lights outside for christmas. My wife added some 'Philips Warm White LED Branch Twig Stakes' in a pot with some evergreens. Looks nice, but the strobe/flicker is really bad. Also, I would call them perfectly neutral, not warm.

I may pick up a new set of white lights just to try again if they go on sale after the holidays.

Anders Hoveland · Dec 9, 2014

markr6 said:
why do all LED Christmas light sets seem to flicker?

Not ALL of them, but definitely most of them. The really cheap ones flicker at 60 cycles per second, which has an incredibly annoying pulsating effect. Somewhat better quality LED lights rectify the current before it goes into the LEDs, these flicker at 120 cycles per second. Better, but if your eyes quickly dart across them the flicker is still noticeable. It is more difficult to find LED string lights that do not have any flicker, but I have seen some.

SemiMan · Dec 15, 2014

Did you move again Anders. Last time you were posting you claim to live in Europe so those lights better be flickering at 50/100Hz

Qship1996 · Dec 15, 2014

Adding a capacitor to the circuit of a full wave set of LED light strings totally eliminates any flicker,even the 120Hz flicker.....these are NOT hard to find,as they are available in some bigbox stores under the Martha Stewart, Ecosmart, and some of the GE brands.Sadly, most people shop and buy based off lowest possible price in the store for seemingly "similar" items......and when you buy cheap,you get cheap- and in the LED strings,cheap strings mean no rectification,a painfully visible 60Hz flicker,and replaceable "bulbs" which begin to rust and corrode their leads rather quickly in outdoor conditions and then the set fails to light.A false economy.

markr6 · Dec 15, 2014

Just for fun, here is a slow motion video to exaggerate the flicker. Regular incandescent lights in back and the LED twigs in front.

SemiMan · Dec 15, 2014

Can't say I have ever seen a replaceable LED string light set and you can bet it would cost more than non replaceable.

markr6 · Dec 15, 2014

SemiMan said:
Can't say I have ever seen a replaceable LED string light set and you can bet it would cost more than non replaceable.

I'm not quite sure what you mean between replaceable and non-, but I won't be swapping out my incandescents for a while. The tint mismatch is actually more annoying to me...and now my wife since I pointed it out to her! HAHA

SemiMan · Dec 15, 2014

Reference to QShip's post.

Anders Hoveland · Dec 15, 2014

It is unfortunate that it is difficult to find LED string lights without flicker. I might have been inclined use them more throughout the house for general lighting.
Because incandescent has been around so long, we are usually inclined to think of an indoor light source as emanating all from one place. Using strings of little incandescent bulbs for general lighting purposes just does not make much sense (for multiple reasons, lower efficiency, lower color temperature light, bulbs burning out). But LEDs lend themselves very well for use as string lights. It does not have to be just for decorative purposes.

That being said, none of the LED Christmas lights I have seen feel the same as the old Christmas lights. Incandescent lights just have a warm glow about them. Many of the "warm white" LED lights seem a sickly yellowish color. The cool white LED Christmas lights work great for an "ice effect", however. When choosing between LED and incandescent, there are definitely pros and cons. I understand that for outside Christmas lighting LEDs are just more practical because the little lights will not burn out, and they can be left on all the time (some houses use Christmas lights as outdoor decorative lighting throughout the year), and use less electricity.

markr6 · Dec 15, 2014

Anders Hoveland said:
It is unfortunate that it is difficult to find LED string lights without flicker. I might have been inclined use them more throughout the house for general lighting.
Because incandescent has been around so long, we are usually inclined to think of an indoor light source as emanating all from one place. Using strings of little incandescent bulbs for general lighting purposes just does not make much sense (for multiple reasons, lower efficiency, lower color temperature light, bulbs burning out). But LEDs lend themselves very well for use as string lights. It does not have to be just for decorative purposes.

That being said, none of the LED Christmas lights I have seen feel the same as the old Christmas lights. Incandescent lights just have a warm glow about them. Many of the "warm white" LED lights seem a sickly yellowish color. The cool white LED Christmas lights work great for an "ice effect", however. When choosing between LED and incandescent, there are definitely pros and cons. I understand that for outside Christmas lighting LEDs are just more practical because the little lights will not burn out, and they can be left on all the time (some houses use Christmas lights as outdoor decorative lighting throughout the year), and use less electricity.

I sure hope they improve and come down in price. Right now between a dozen sets outside and two christmas trees inside, I'm burning about 1200W/hr! That's about $0.18/hr where I live. Not crazy, but it adds up to about $37 extra for the entire holiday season (I don't let them run overnight)

I've seen the cool lights which acheive the ice effect you mention and can look nice. I also see a lot of the RGB lights which I think are horrible. Just personal prefernce, but it looks like something to put up at a circus or freak show to me. I actually don't recall seeing any all-white LEDs...which may be a good thing. Maybe I've seen them but just couldn't tell they were LEDs?

Anders Hoveland · Dec 15, 2014

markr6 said:
I also see a lot of the RGB lights which I think are horrible. Just personal prefernce, but it looks like something to put up at a circus or freak show to me.

Even when it comes to colored Christmas lights, there are pros and cons between LED and the old incandescent ones.
The wavelength of red they typically seem to use for colored LED Christmas lights often seem a bit orangish-red. In contrast, the red filtered incandescent bulbs seem a deeper red, maybe a little magenta, maybe just a little pink, but to me they still seem more saturated than the orangish-red LED lights. Then there is blue. Blue LED lights seem like a more saturated deeper blue, but it is also a little harsh, difficult to focus on. In contrast, the blue on the old Christmas lights had a much softer quality, though just a little whitish. It is not that one is necessarily better than the other, aesthetically, but there is a moderately substantial difference in appearance.

Qship1996 · Dec 15, 2014

SemiMan said:
Can't say I have ever seen a replaceable LED string light set and you can bet it would cost more than non replaceable.

are you in the USA- I am guessing not, because EVERY inexpensive LED light string sold in the USA bigbox stores uses replaceable bulb LEDs,which lead to the rust/corrosion issues and therefor a failed string of lights many here experience- you have to shop the specialty,mostly online, dealers to purchase "commercial" sealed,one piece, single injected molded,non replaceable full wave rectified led light strings which are much more expensive{and higher quality} than what you find at the local wmat,depot,or lowes.See here for where I buy my sealed,fully rectified quality sets.. www.holiday-light-express.com

LED Christmas Lights PWM?

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