THD In Light Bulbs

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.