Detecting AC lights with sensor?

This may be a strange question, but is there such thing as a sensor to detect AC lighting. Not current - lighting. My logic is a little lengthy so, I’ll omit. For now, all I need to know is does such a device exist - even if it’s not ST

There are many “lux sensors” which can detect how bright it is. Some work with SmartThings. These are popular for turning on lights only when it’s dark, for example. But you can use it the other way around, to determine if dumb lights were turned on or not.

There are also devices that can be wired inline to monitor the current being drawn, but you indicated you weren’t interested in those, so it appears you’re looking for the light level in the room?

Or am I not understanding the question?

Anyway, it comes down to the specifics. Also, we would need to know what country you are in and whether you have a SmartThings/aeotech hub or not, because the device selection does vary.

Just realized, perhaps you are using “AC“ as an abbreviation for something other than “alternating current“?

For example, if you are using it for “air conditioner“ then the following zwave sensor is specifically designed to detect LED indicator lights. It used to work with SmartThings, but I can’t remember if there’s an edge driver for it or not.

You can also build your own one of these: it’s how little robot cars tell red lights from green lights, for example. But that’s a much bigger project.

Anyway, I know you didn’t want to overburden us with too many details, but I feel that a few more details might help us help you better. :wink:

AC = alternating current.
In the US
Yes, I want to determine if dumb lights were turned on or not.

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Then a lux sensor should work. There are lots of these: zwave, Zigbee, matter…

  1. Eve has a thread-based motion/lux sensor that works with matter, so should work with SmartThings out of the box with no custom code required.

If this is your first matter device, read the community FAQ so you’ll know what you’ll need:

FAQ: What do I need to add a Matter device to the SmartThings app? Do I need a bridge router device?

  1. If you prefer a plug-in sensor, third reality has a Zigbee option, but that one does require a custom edge driver, which you can get from them.

  1. And yet another option is an Aeotec multi sensor, which is z wave. Some models can run off USB power or batteries. They have several different models with slightly different features. The new Tri sensor 8 is supposed to have the most accurate Lux sensor.

The Aeotec also has an optional add-on recessor plate which Some people prefer the looks of.

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Oh, and in case you’re curious, the usual starting point for this use case is

Less than 10 lux → light switch is off.
More than 50 lux–> Light switch is on.

But it can vary, depending on how bright your lights are, the position of the sensor, whether there are windows that let in outdoor light, etc.

Sometimes it just takes some trial and error to get everything adjusted so it triggers when you want.

THIRDREALITY also makes a Matter over Wi-Fi Smart Nightlight that has a lux sensor similar to the Eve.

Requires installing the vendor’s Edge driver found here.