LEDs and Smart dimmer switches


New to home automation!

What is the maximum number if LED down lighters you can have using something like the Z-Wave Fibaro Dimmer 2? I have 20 down lighters in a conservatory that I would like to control. I haven’t bought the lights yet so would Halogen be a better option?


If I remember correctly its a max of 250w… so it depends on the bulbs that you are putting in. But lest say you are using 4w bulbs, that means 62. Hehehe you should be fine.

The halogens are normally higher watts which means you will have less.

Thanks for the reply,

Having read some more it would seem if you use LEDS on a any dimmer you have to divide the max wattage by 10! So if it’s 250w dividing by 10 obviously gives 25w which would mean 5 5w lights!

Very confusing!


Where did you read that?

I have a Dimmer 2 controlling 12 GU10 LEDs with no issue. I’ve not swapped them all over to be dimmable so the Fibaro is in on/off mode but i’d not thought that’d make any difference.

Yep I have 10 x 7w (all dimmable) attached to 1 dimmer and Ive had no issue for well over a year so not sure where you read that?

Are you not more thinking about a heat issue?

IE does your fixture provide the right cooling for LED’s?
Quite a nice article giving the basics:

But this will have nothing to do with the dimmer, in fact all it means is that the LED bulb might not last the 25 000 hours that its intended.

This is where I got the info on LEDs and dimmer switches.


I was also told by LightwaveRF that max they support on their dimmer was 10 lights per gang.


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If it’s an older switch and doesn’t give a specific LED rating, then yes, the VA in LEDs that the switch can support will Typically be much lower than the wattage for traditional incandescent bulbs. The reason has to do with something called “inrush current” and it’s because the LEDs have a very high current draw when they first start up, then they drop down to the regular operating level. The usual rule of thumb is 1/3 of the rated incandescent value as a maximum for LEDs. But there are many electricians who use a rule of 1/10 just to be absolutely safe— especially when they are writing articles!

That said, most of the newer devices will show two ratings, one for “resistant” loads ( Halogen or incandescent) and one for LED loads, which are “inductive.”

Also, because of the different physics involved, many devices will have a minimum load rating, typically 20 VA, for inductive loads like LEDs. So there may be a minimum number of bulbs required, or else you have to add a separate device called a “bypass”.

So just check the specification for each device carefully so you know whether you are looking at the LED specification or not. :sunglasses:

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BTW, the Fibaro Dimmer 2 Is a very sophisticated device and can determine for itself whether the load is resistant or inductive and re-calibrate how it handles the inrush current. Very clever, and it’s why you will see that its specifications are much more similar than for most switches.

Dimmer 2 is equipped with an algorithm of smart light source detec- tion. Depending on the connected type of light source, it automat- ically adjusts an optimal control mode (leading edge for inductive loads, trailing edge for capacitive or resistive loads). The procedure of learning the light source type is called calibration.

So spec on the Dimmer 2 says it can control up to a max 250w, does that mean it can handle 20 x 12.5w LED downlighters?

Sorry if these are dumb questions!


Just seen that applies to incandescent and halogen!

I have one more question if that’s OK?

Are there any limitations on the number of LEDS and using a relay to turn them on and off?

I’m now thinking about simplifying things. I’ve found a non-smart dimmer that can handle up to 30 LED downlights and then use a relay to schedule switching them on and off.



The limit isn’t the number of LEDs, but the load across those LEDs.

You’ll have to think carefully if you you mix a relay with that dimmer. eg, will the dimmer work if the relay is off.

Point taken.