THD In Light Bulbs

I have replaced a 40w incandescent light bulb with a 12w LED light bulb. The new LED is way brighter. In fact, the box says that it's a 75w equivalent. The box also shows something interesting:

Power Factor >.90  
THD: <35%

I've read that LEDs are essentially diodes. How does this affect noise in the mains? Do LEDs inject more, less, or the same amount of THD into the mains as incandescent/fluorescent lights? 
LED=light emitting diode
Are you hearing more noise with it on? If not, just enjoy your music.
Best to turn off, unplug  EVERYTHING in your house for true sonic enjoyment.

That's if you follow the "keep the power pure" philosophy.

Yeah, I noticed that too. LEDs are not essentially diodes. LEDs are actually diodes. 

But hey don't take my word for it. Try reversing direction, see how that goes.
If you are not using a dimmer, then I would not get too worried. It's just another small switching power supply on your AC line, and odds are you already have quite a few (all those USB chargers, and they can be worse).

If you have a dimmer, then yes, things could be noisier as the power supply in the bulb will have capacitors on the front end which will result in higher peak currents when the dimmer turns on (120 times a second, 100 in some parts of the world).

There are some bulbs/lights that do not have switch mode power supplies in them, but simple linear regulators. They are common in low cost flush mount ceiling lights, but not very common in bulbs. I would avoid most as they can have lots of invisible flicker.
Can someone elaborate on smart light bulbs?  I recently added 8, color changing, dimmable, smart led bulbs from sengled...

That is a link to a highly technical article, that is itself really only applicable to one IC / control architecture. Most EEs would not understand the subtleties of it, let alone most people here. It is really not applicable to the ops question.

Basically a switching power supply, akin to a USB charger, and about the same power level as well.

I don't see anything about EnergyStar for these bulbs. If they were EnergyStar, they would have to meet some minimum power factor requirements that would normally mean less harmonics on the AC line. Since they don't appear to be, they could be poor (akin to those USB chargers).

b_limo1,065 posts01-04-2020 12:01pmCan someone elaborate on smart light bulbs?  I recently added 8, color changing, dimmable, smart led bulbs from sengled...

Depends on the light. I've heard and measured on a scope what compact fluorescent light bulbs do an AC line and they are horrible.

Others have reported issues with dimmable LED's. The traditional wall dimmer is also a potential noise source.

I try to keep everything that switches outside of my clean power zone. This includes network routers, etc.
audiozenology"That is a link to a highly technical article, that is itself really only applicable to one IC / control architecture. Most EEs would not understand the subtleties of it"

It’s much more science-based, factual, and authoritative than sites such as wikpedia and it’s level of math is well within that which a real EE could understand it’s not fair to dismiss with "a wave of the hand" real science just because it might confuse some and even you perhaps!
It would be within the realm of an EE if they had the experience and knowledge on the topic. EE is a big area and most EE's would not have the specific knowledge in the area for this article to be of much use without some extensive studying. Heck many EEs who work in this area do not understand what's discussed very well.   I am very qualified to make that statement. You are not. It's not really appropriate to the ops question as it only deals with one particular implementation that could be one of numerous used in a bulb and says little about PF and THD of actual LED bulbs. 

Again, if you are going to troll me, which you are obviously doing as you respond almost every post I make in new threads, then you need to step up your technical game.
My biggest concern is that LEDs may inject more noise into the AC line than incandescent light bulbs. If that's the case then I'll continue to use incandescent bulbs. Also, I've recently installed Akiko Audio and Perfect Path Technology products in my system that helped clean up noise in my AC. It's important not to counteract their effects. 

  • If you have no dimmer on the line, then the incandescent bulb will inject less noise.
  • If you have a dimmer on the line, but the dimmer is on full, the LED will likely inject more noise. It will depend on the dimmer and LED bulb.
  • If you have a dimmer on the line, but the dimmer is not on full, the LED bulb will inject more high frequency noise, but the incandescent bulb will inject more low frequency noise (as it will be drawing 5-6x the power). I can't comment on how your specific equipment will behave.

Unfortunately there are no absolutes, but this is about as good a guideline as can be given.
Thank you @audiozenology. That summary was all I needed.

 My television and computer monitor are full of LEDs...oh well.
If it wasn't LEDs it would be compact fluorescents or vacuum tubes. They would use more power and there would be even more noise. LEDs are not noisy, just the power supplies used to drive them.
There is more to electronic noise than the THD.   Power factor also comes into play.   The OP's bulbs  seem to be pretty good with a Power Factor >.90.   Many of the cheap ones are not Enerystar rated have a power factor ~50%.   That means that half of the power going in is wasted and the unused "power" is dumped into the neutral leg.  And while the THD: <35% does not sound that good hopefully it is much <35%.  A good bulb can be ~ 10%.   But generally if a good manufacturer cares about their design power factor and THD are both optimized.    

So the take home message is you should look up the specs before you start swapping out your incandescents and don't buy the cheapest dollar store brand bulbs.

No, that is not what it means. A power factor <1 simply means that current and power are out of phase. This does not mean that there is "wasted power". Power factor does not give any definitive indication of wasted power.

That means that half of the power going in is wasted and the unused "power" is dumped into the neutral leg.

Power factor can give an indication of the potential for noise (in the form of THD), but only if you know the circuit. The THD of up to 35% is the important figure of merit in this case. It is unlikely to be << 35% or they would have just used a lower number in their marketing.  At this low power level, power factor will not have any appreciable impact on other equipment but the noise from high THD may.
Audiozenology-If dedicated lines are used for the audio system, separate from the lighting electrical, will the dimmer still affect audio quality?  Leon
One thing to remember with anything that has THD is it only applies to audiophiles and power company managers. No one cares if their light bulb is a little bit dimmer than it is supposed to be or that your hairdrier could be more efficient if they put the most basic power reducing circuit instead of just one diode to block 1/2 of the sine wave.

The take home message is that after your dirty power component sucks out the small amount of the 60 Hz sine wave it needs what is left behind is a distorted non sine wave (dirty power). What is left behind in your lines plus the fresh supply of the good power coming from the generator is what your audio equipment gets. How far does the dirty power what is left over get? Theoretically it goes back into the grid where it gets averaged back in to everyone. But in reality it is worse the closer you get to the source. That is why people get dedicated power lines for audio but still claim they can hear when a neighbor is running a hairdrier down the street.


An incandescent light bulb is a purely resistance load. There is no noise.

Thank you jea48. That's good news.The consensus shows that incandescent lights may generate less noise compared to LED or no noise at all. 
@orthomead I have my stereo on two parallel 20amp lines with no other household devices.  Unfortunately I could still get some electrical feedback from other devices on different lines (when I turned on an LED light I got a slight music dropout, perhaps due to the router I was streaming music through?).  Eventually I got a power regenerator (an old Elgar as recommended by Atmasphere), put it on one of my lines, and that stopped the problem.  
Those tests show how much interference is emitted through the air. It's very interesting nonetheless. 

Here are a couple more videos demonstrating similar tests: