Led dimming

[Mist78]

Can somebody help me understand what my dimmer is capable of please?
I've recently ordered an aurora aone 250w smart dimmer (because I'm tired of my smart bulbs becoming inaccessible when people flick the switch, so this way I just use normal dimmable bulbs).

The minimum load is 10w, the maximum 250w.

From what I've understood when it comes to halogen bulbs there should be no issues (obviously as long as the total load is less than 250w, although apparently ideally less by 30% to account for the start up load?).

However I'd prefer to use LED bulbs from now on (currently it's a 1 bulb fixture). If I buy a 10w dimmable LED bulb should that work?

To be honest I've forgotten my school electrics knowledge so from what I understand dimmers work by varying the voltage, but I have no idea how or if that affects the wattage, so my thoughts are along the lines of can a 20w bulb only be dimmed by half if the minimum load is 10w, and a 10w bulb not dimmed at all?

The other thing is I've read 2 similar but slightly different bits of information regarding maximum load using LEDs. One states that because they have a high start up load you should assume each fixture will use 100w (even if I used 4 x 5w bulbs?), the other states you should divide the maximum load by 10.
So I'm now confused by how many LED bulbs I can use, and at what wattage.

Thanks

 

[bernardgreen]

Dimming LED lighting with off the shelf dimmers and LED lamps can be prone to problems.

Halogen lamps are dimmed by reducing the effective supply voltage. Effective because the filament of the halogen lamp averages out the voltage if it is a chopped supply

The red is the waveform of a leading edge dimmer, and has and effective AC voltage approximately half that of the green pure sine wave waveform. This half voltage will reduce the power to the lampt to 1/4 Watts = volts X amps. Amps = voltage / resistance ( of filament ) Hence Watts = Voltage squared / resistance

A similar formula applies when the dimmer is trailing edge.

More info HERE

LED elements in LED lamps are dimmed by reducing the current through them but the equation Amps = voltage / resistance cannot be applied to an LED element as the effective resistance of the LED element is very close to zero when the LED element is lit.

In an LED lamp there has to be a driver that controls the current driven through the element irrespective of the voltage of the supply. The one exception is when a resistor is in series with the element and this resistor controls the current. Changing the supply voltage will then alter the current through the resistor and LED element and hence the brightness.

To dim an LED lamp requires that the driver in the lamp can recognise that the waveform of the supply is not a pure sine wave and alter the current driven through the LED element accordingly

In some drivers the amount of current driven through the LED element depends on the shape of the waveform. ( where the chop point occurs determines the current )
In some drivers the amount of current driven through the LED element depends on the effective voltage of the supply and not the shape of the waveform.

Error corrected

 

[boringoldcodger]

Deleted, as no longer relevant.

 

[bernardgreen]

I believe he meant "lamp" rather than "LED"

Thanks for spotting my brain's error. It has been corrected,

 

[ericmark]

It would be really good if the bulbs told you how they work however all they do is (by law) state if no dimmable.

There are two ways to power a dimmer or any other electronic switch, one is to connect a neutral., the other is a small current through the bulb. The latter needs the bulb to leak a small amount of current without lighting.

However the bulb does not need to say if it has the leak current built in, so with some you need a small capacitor in parallel with the bulb.

Why some bulbs flicker I don't know, I don't have dimmer switches, but I do have electronic light switches with out a neutral, one can hear a relay operate so would not expect to flicker, but the G9 bulbs do.

So you have to read the dimmer switch instructions including the list of compatible bulbs, which in the main means using expensive types.

 

[Mist78]

OK, so I may have completely misunderstood but from what I've read, at the moment it's not always clear which LED bulbs will work for dimming with which dimmer, if any will.
Although there should be some that work with the dimmer I've bought as it states both halogen and LED bulbs up to a maximum load of 250w, but I guess it'll be trial and error.
And I'd probably be better off with as high a wattage LED bulb as I can get away with, at least while I'm only using 1 bulb.

The thing I'm not fully understanding though is the 10% rule. Do LED bulbs really spike that heavily that you have to cut the maximum load that much?
In which case I assume I'm left with being able to get up to a maximum of any combination of LED bulbs up to 25w?
So as it is at the moment with only 1 fixture/1 bulb I would need an LED bulb over 10w but no more than 25w. And then later on when I install a new light fixture which can take 4 bulbs, I'd have to switch over to say 4 x 5w bulbs.