Hum, buzz, induced noise - it is possible to control and isolate electrical noise, but it requires willingness to make changes.

A decade or so ago I listened to an engineer describe how he designed and built a sound recording studio with the specific objective of eliminating electrical noise. It was successful, and he related a story about a guitarist that came in to use the studio. He was accustomed to adjusting his amp until he could just barely hear the background buzz. Powered up in the studio, he was concerned that his amp was not working. He turned the volume up, then turned it up some more. No buzz or crackle, it seemed like it was off. Turned it up some more. Still quiet. Someone suggested he try playing something, and the amp responded at huge volume. There just was no AC hum, it was completely clean sound.

Electrically noisy equipment can be tamed and silenced. Shielding, well configured grounding and electrical isolation techniques can be very effective.

As I posted previously, dimming CFL and especially LED lighting by messing with the AC waveform (aka 'dimmers') is bass ackwards. Provide clean power to the lighting and have the lighting itself control brightness. Use high quality DC electronics for the LED dimming and control.

The glowing filament inside an incandescent bulb is an electromagnet. When the AC current flows the filament develops an oscillating magnetic field, 60 magnetic cycles per second.

With full brightness the AC current (not voltage, current) through the filament ramps smoothly in a sinusoidal manner. Sometimes a bulb filament will vibrate sympathetically with this alternating magnetic field even at full brightness but generally the sound is inaudible.

If you bring a strong magnet near the bulb surface you may be able to see the filament vibrate visibly.

When the power to the bulb is 'electronically' dimmed the previously sinusoidal AC current waveform becomes bastardized. The magnetic field now jolts and collapses repeatedly, 120 times per second. The glowing filaments can vibrate sympathetically and conduct the vibrations to the lamp base and the fixture.

Do the lamps that buzz when dimmed have a filament design that zigzags or loops around inside the bulb? Sometimes that can magnify the magnetic resonance effect and become more audible.

The bulb construction is such that it acoustically conducts the filament resonance more than a different brand or bulb filament design. If you find a different bulb that dims with less sound, change the bulbs.

Curiously, here is a patent describing the magnetically indused vibration of the support wires for the filament. I found this interesting; The frequency of the noise emitted by the lamps was in the range of 4,000 to 15,000 Hz.

That would be very much in the range of human hearing, but at the high end.

Tips from around the Internet;
Lutron Lamp Debuzzing Coil (LDC)

http://forums.mikeholt.com/showthread.ph...8921#post958921

I haven't disassembled an LED bulb to look, but it's really doubtful they use such expensive (copper) and space consuming tech. More likely a simple diode or similar.

The cheapest/simplest way I can imagine to build an LED bulb from scratch, would be to just insert a power diode in series with about 80 LEDs (120V operation), assuming each LED drops 1.5V from input to output. Adjust the quantity if the drop is different.

EDIT: actually, the power diode isn't needed, since each LED is a diode already!

Now that bulb will flicker at 60HZ, so it could be improved with a full-wave rectifier, aka. four diodes instead of one, so that it flickers at 120HZ instead. Add a nice capacitor or two to blur the flicker to imperceptible levels.

Commercial bulbs are undoubtedly fancier than that. I really should sacrifice one to the gods of curiosity some day soon!

The two most common versions I've seen are
1) proper switchmode supply (controller chip and inductor) operating at a much higher frequency than the mains.
2) series inline capacitive dropper limiting the current like a resistor, but with an almost 90 degree phase angle between voltage and current to avoid much real power lost,followed by rectifier bridge and smoothing cap. Resistors to limit inrush current and to discharge caps - mainly in the cheap Chinese ones.

For looks inside various LED bulbs I can recommend BigClivedotcom on youtube

Edit: He just posted on dimming LEDs with mains dimmers - https://www.youtube.com/watch?v=fWh2obSY0dQ

There's always the option of using 12v DC LED's in series, and then power them all via one good-quality transformer. (the same system that is used for halogen spots) Or use a micro transformer of good quality per light, but then you need adequate space behind the ceiling to tuck it away.

Thanks for all the information, but my takeaway after reading all of this and looking at other sources online and trying some things out is that it just depends on the equipment.

In our master bathroom we have recessed lights and vanity lights. The recessed lights just had a random selection of bulbs that the contractor put in there and I never bothered to replace. Some regular light bulbs, a BR30, and one vanity bulb for some reason. These didn't buzz. Our vanity, on the other hand, consists of two fixtures with two bulbs each, and were regular 60W incandescent bulbs, and those bulbs buzzed like crazy when dimmed.

These lights are all controlled by the same two dimmer switches, and had the same behavior when being controlled by their previous, cheaper dimmer switches.

So last night I replaced all the bulbs in the bathroom with Cree LEDs. Standard A19 bulbs in the vanity and BR30's in the recessed lights. The result is that the vanity doesn't buzz (or has the faintest buzz that I don't think I'd notice if I weren't listening for it in a silent room), and the recessed lights are buzzing terribly. It's louder than any light buzz I've experienced.

I think I'll be returning the BR30's and trying another brand. It's too bad, the Cree bulbs are starting to look really sharp these days. I might try one of the ecosmart bulbs and then maybe a more expensive one and see which one is the winner.

Regarding color temps when dimmed:

I find it strange that all my older Cree bulbs give me a more incandescent behavior when dimmed, and the newer ones perform more like you'd expect from an LED.

Perhaps you meant to say 'in parallel' ?

Yes. That. I always mix those terms up.

An update:

I went out and bought two brands of BR30 bulbs. I picked up a 6-pack of Ecosmart (Home Depot brand, I believe) for $30 and a 3-pack of Philips for [I believe] $21.

The important thing about the Philips bulbs is that they're advertised as having a "warm glow effect." It's just saying that it mimics the effect of a dimmed incandescent bulb. That sounded like what I was looking for.

Long story short, I hated the Ecosmart (the color was just not great), and I loved the Philips. The warm dim was subtler than I expected, and just what I was looking for. I still feel silly about it, but it's what I'm used to and my wife preferred it to, so that's what I'm going with.

The only problem was the price. At $21 or more for 3 bulbs, it was going to be an absolute fortune to replace all my BR30's (I have a ton of them in my house - around 35 at last count). Fortunately, Amazon came to the rescue once more. There's a seller offering 24 bulbs for $135, coming out to about $5.63 per bulb, which is pretty good. My favorite thing about it is that it's clearly a box that's intended for a Home Depot show room, because it ships as a display case, including the standup to advertise the bulbs, with pretty clear HD styling.

At that price, I'm actually considering buying a second pack to fill in the remainder of the cans, then having some on hand for future recessed installs, or I could sell the rest at my upcoming yard sale and come out way ahead of buying the 3-packs.

Oops, I forgot one last thing:

I put Philips warm glow BR30 and A19's in all the fixtures in my master bathroom. No buzzing! I don't know if there's just something about those Cree bulbs, but the difference is drastic.

The delta is about $33 between the $135 for 24 display pack and 8 packs of the $21 three pack, by my math.

Delta of $1.40 per bulb is not quite a fortune. Diner out, perhaps.

Thanks for posting the results. Will be handy if others are looking for that form factor in LED dimmable light bulbs.

True, but one requires me to go to Home Depot, load 8 packs of bulbs into a cart, scan them one by one (because they never man the checkout lanes at my store), and drive them home where I unload all the bags.

Or, Amazon Prime delivers a big box of 24 bulbs to me in two days, I save $33 (and get some dinner), and I don't have to do anything. Winner!

I've never been a penny pincher (even when I probably should have been), but saving $33 here and there adds up tremendously.