LEDs are buzzing, seems to be bulb specific

[TullioK]

I know this is a boring question that must get asked a lot but I promise I have done some research and cannot find an answer that fits with my experience.

I've recently moved house, had it rewired and I've fitted Philips LED bulbs throughout. Most are from their 'Warm White' range and some are from their DimTone range.

I've used these bulbs before and been pleased with them, but this time I notice some are buzzing quite loudly. It's not just the ones on a dimmer, and it seems to be bulb specific. ie. the nosiest bulb is noisy whichever fitting I put it in.

If it was just one bulb I'd assume it was a duff and replace it, but it's more like 20% of them. Has anyone else had this kind of experience?

Thank you

 

[oldbutnotdead]

What sort of dimmers are you using, and are your LED lamps designed to be dimmed by the dimmers you have installed (LED dimming is a bit complex. Tungsten can be dimmed by cheap nasty triac things, LEDs have more specific requirements).
The lamps that have gone noisy- have they been used in the dimmed circuits?

 

[TullioK]

Thanks for your reply. I will have to check with the exact dimmer type. I must admit I assumed that a top brand bulb would be compatible with any modern dimmer.

If the dimmer is not compatible with the bulb, do you think it might have damaged the bulbs and so even changing to the correct dimmer would not switch this?

It's possible that our electrician could have used some of the non-dimmable bulbs with the dimmer to test the circuit. I hadn't thought of that before, though I think it's unlikely.

Thanks again

 

[oldbutnotdead]

Assume makes an ass out of u and me. As above, LED 'lamps' have a certain amount of electronic gubbins included in the package, they require a far more precise supply specification than a bit of wire in a vacuum.

 

[fluorescence]

I'd consider Philips to be no longer a "top brand" of lamp. It's entirely possible they're just noisy due to poor/cheapened-down circuit design. I'd start by getting one or two replacement lamps from another brand and seeing how they do.

 

[bernardgreen]

I notice some are buzzing quite loudly.

The bottom line is that there is nothing designed into the lamp for the purpose of creating sound.

The one device that most often creates noise is an inductor. Wire wound onto a magnetic core.

The sound is created by the windings vibrating due to the alternating current passing through them .

The windings in a well made inductor will not be able to vibrate as they will be tightly wound and/or encapsulated in a resin.

 

[Taylortwocities]

I assumed that a top brand bulb would be compatible with any modern dimmer.

Alas, successful dimming of LED lamps (even "top-brand" one) requires co-ordination between the lamp and the dimmer. Many dimmers require a minimum load for them to work, some are trailing edge, some leading edge. There are specific dimmers for LED loads and most reputable manuafturers provide a compatability guide.
Oh look, so does Philips! https://www.lighting.philips.co.uk/consumer/long-lasting-led-lights/dimmable-led-bulbs

 

[bernardgreen]

There are specific dimmers for LED loads and most reputable manuafturers provide a compatability guide.

An LED lamp dims its light by the driver in the lamp reducing the effective DC current that it drives through the LED element. Sounds simple but....

Only when the DC current driven through the element is smooth is the light output is directly proportional to that current.

But most drivers control the current by means of a switch mode controller which produces a DC current that fluctuates at a high frequency. The light perceived by the human eye is as bright as the highest peak of the fluctuating current.

The drivers integral to the better quality lamps do smooth the current through the element which does not create peaks of brightness and gives better control of the perceived brightness. This requires extra component in the driver and can produce more heat than the typical switch mode controller does.

The problem facing designers of low cost domestic lighting is how to get information of the dimness setting from the dimmer switch to the driver in the lamps when the only connection is the Neutral and Switched Live of the mains wiring.

The only way is for the dimmer to change the shape of the mains voltage waveform from a sine wave to a chopped sine wave. The sharp change of voltage at the chop point can cause instability in the operation of the driver in the lamp.

 

[TullioK]

The only way is for the dimmer to change the shape of the mains voltage waveform from a sine wave to a chopped sine wave.

Thank you for the explanation. So the dimmer switch is really just sending an instruction to the lamp, which takes care of the current modulation itself?

Alas, successful dimming of LED lamps (even "top-brand" one) requires co-ordination between the lamp and the dimmer. Many dimmers require a minimum load for them to work, some are trailing edge, some leading edge. There are specific dimmers for LED loads and most reputable manuafturers provide a compatability guide.
Oh look, so does Philips! https://www.lighting.philips.co.uk/consumer/long-lasting-led-lights/dimmable-led-bulbs

Thanks. I've had a look at the information Philips provide, including that link. Unfortunatley the symbols they say should appear on packaging don't appear on the bulbs I have (which just say dimmable!) and the list of compatible dimmers doesn't include British General, which is what I have (am I missing something there)? I have now at least established that the Philips bulbs are either compatible with all dimmers or trailing edge only and I think my dimmer is leading edge (again not completely clear on the spec!). So that could be the cause on the dimmer noise.

This doesn't seem like something that should be difficult to get right but clearly this hasn't been my experience...

As for the non dimmable bulbs that are making noise, I guess I'll just have to try other bulbs until they don't, as it's only a few bulbs that do it.

Thanks again.