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Why do smart switches have 2 different wattages based on LED and Incandescent bulbs?

I have found information regarding Dimmable light switches which makes sense because of the dimmer control can cause harmonics and distortion that occur in the LED driver that powers the LED lights when over 150 watts are passed through the switch. However I can't find anything on a smart switch which is not dimmable and just on / off no dimmer control electronics.

I want to change the switch to my basement lights to a smart switch (on / off, NO DIMMER) it states 15amps, 150 watts max LED and 600 watts max incandescent. I have (5) 4 foot T8 shop lights (no ballasts) each have 2 LED bulbs @ 18 watt per bulb (total 180 Watts for all shop lights) and (3) 14 watt regular screw in LED light bulbs (Total 42 watts).

Total watts for entire basement lighting is 222 watts. I was looking at total watts not for illumination purposes but to make sure I did not put too much current through the switch and burn it up.

A 15amp switch at 120 volts is 1800 watts - why would I be limited to such a low LED max watts?? and what would happen if I used the smart switch anyway.

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    Can't ans your question about why switch has a different wattage rating for LED vs Incandescent bulbs. Use a different smart switch. Leviton makes a smart switch, non-dimmable, rated at 600 watts for LED. Found on HD site.
    – Programmer66
    Commented Dec 16, 2021 at 17:07
  • I have a Honewell non-dimming ZWave rated for 1800W or 960W incandescent but with no specified LED rating. Does that mean they didn't test it with LEDs? Or they don't think LED inrush is as big a deal as OP's manufacturer does? Or it was designed before these concerns came to light?
    – jay613
    Commented Dec 16, 2021 at 17:20
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    The Leviton incandescent rating is 1800 watts, I provide the link to the specific one in my answer below.
    – Programmer66
    Commented Dec 16, 2021 at 17:22
  • The reason for the smart switch is that I have a rear door from the backyard and there is no switch at that entrance. I am tired of coming in the back door and traversing the dark basement to reach the switch at the bottom of the basement stairs. Currently there are 2 switch, top of the stairs and bottom of the stairs. I did not want to run wire to the back of the basement and add a 3rd switch. Easier to have Alexa turn it on from my phone or voice command.
    – Don
    Commented Dec 21, 2021 at 19:35

3 Answers 3

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I'd actually argue the proper answer is "Doesn't matter why, just get a different switch", as already noted in another answer.

But to answer "why", you have to realize that a typical residential smart switch does not have an electronically activated mechanical switch - a.k.a., a relay. If it used a relay then the only real issue would be maximum current, whether in user or at start (inrush).

Instead it switches using various purely electronic components. These components can themselves be quite sensitive to the load they are switching. An incandescent light provides an extremely consistent (except for inrush) level usage. An LED light (or technically, the driver for the LED light) uses power differently. This has a number of effects, one of which is referred to as Power Factor. Power factor, as well as other side-effects of LED lighting, can result in purely electronic switches having a limited safe & reliable switching capacity compared to straight resistive loads such as incandescent lighting.

While this is a new problem (relatively speaking) for lighting, the typical ratio is 1/3 or 1/4 of the incandescent switching capacity available for switching LEDs. Since a typical LED light uses far less total power than equivalent (in terms of lumens) incandescent lighting, for the typical residential usage this is not a problem.

Note that this is really nothing new. Timers and other specialty switches have long included different ratings for use with motors and other equipment than for lighting. The only difference is that now specific types of lighting have different ratings as well.

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See this link Why Different Wattage with Smart Switch as to why the different wattage rating.

To solve your problem, use a different smart switch. Leviton makes a smart switch, non-dimmable, rated at 600 watts for LED. Found on HD site.

Link to Smart Switch. Rated for 600-Watt LED and CFL Dimmable bulbs and 1800-Watt incandescent bulbs.

I would not exceed the wattage rating of the switch you were thinking of using. Bad things can happen. If operating by remote, you won't necessarily be there to see it happen.

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  • Wow, nice. That switch is very specific about its capabilities and I am led to believe that they designed it to handle surge currents without failing. I also read between the lines that LEDs do commonly draw a stronger inrush current than incandescents.
    – jay613
    Commented Dec 16, 2021 at 17:24
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Incandescent lights draw a higher current when cold, and this results in a very brief (milliseconds) inrush current when first turned on that is higher than the current implied by the rated bulb wattage. This effect is not enough to dangerously heat up wires but it may be enough to damage your solid state switch if you were to use 1800W worth of incandescent bulbs.

Some LED lights also exhibit an inrush current. I know less about the mechanism, and this is complicated by the fact that not all of them do, and the technology is changing. But I suspect the rating of your switch is derived from a conservative approach to the behavior of widely available LEDs at the time the rating was produced.

Some (admittedly, unrealistic) solutions:

  • install a relay, with suitable capacity, off your smart switch.
  • see if maybe your own LEDs don't produce this problem. You'd need an oscilloscope with CT probes.
  • Rethink it. 200 watts of LED lighting a a LOT for a basement. Install smaller lights? TBH I have a brightly lit basement too, I get it. But I don't have a smart switch on it. Why do I need "smart" control for so much light?

Note that there is another answer from @Programmer66 with a realistic solution. :)

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  • "Watts" as a unit of measure for illumination is rather meaningless these days. I've got 11 LED strip lights in my garage/shop. I have no idea how many watts they draw, but they each put out 5000 lumens of light. Yes, I have 55000 lumens in my garage, and I've got 4 more lights to put up. No, my eyes aren't quite as good as I'd like them to be. Watts is important to ensure you're not overloading circuitry (or switch gear), though, and each of those fixtures is 60 watts. I'll have a grand total of 900w of power draw, so I should be good on my 15A breaker & switch.
    – FreeMan
    Commented Dec 16, 2021 at 17:32
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    I think what underlies your comment is that LED lighting efficiency varies greatly and lumens output is a more useful measure than power draw. But I think I am nevertheless safe in my assertion that 222W is "a lot", unless OP has scoured the earth for the world's worst LED lights, or is running an underground grow farm. :)
    – jay613
    Commented Dec 16, 2021 at 17:45
  • My garage begs to differ with your assertion of what "a lot" is! ;) Also, I'm pretty sure I'm getting more than 4x the lumens from my 900w that the OP is from his 222w. And yes, lumens output is far more interesting and useful than power draw, at least from the end user perspective.
    – FreeMan
    Commented Dec 16, 2021 at 17:50
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    @Matthew 5000 lumens / 60 watts = nope. :( Frankly, that wasn't a factor in deciding on my lighting choice. I opted for max lumen/$ purchase price. Sure, that may be short-term thinking, but it's what I went with.
    – FreeMan
    Commented Dec 17, 2021 at 17:01
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    My basement is L shaped, I use a screw in bulb fixture at the top of the steps where there is a short 5 foot walk way and coat rack and another at the bottom where there is foyer and cubbies. In the main space I have 4 shop lights to light the length of the long L which spans 40 ft long by 30 ft wide and 1 shop light to light the short part of the L. The last screw in bulb is over the furnace and hot water heater a single bulb is sufficient when servicing the oil burner. So although some think 222 watts is excessive it really is not when considering the configuration and size of the basement.
    – Don
    Commented Dec 21, 2021 at 19:32

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