Please start a new thread for this if you want to discuss it further so we don’t clutter up the FAQ.
But there are a few options.
Zemismart has a zigbee 3.0 4” that is supposed to work with ST. I don’t know if it’s been tested with the new V3 app.
- Tuya has a similar Zigbee device, a little smaller, the same caveats apply. (Note that this is one of their new Zigbee line, not a Wi-Fi device.)
- Philips hue makes a 4” model. Integration with SmartThings is through their hue bridge.
There are quite a few cheap brands that make these for the Chinese market, but I am always uncomfortable about wiring in some thing that doesn’t have safety certifications, so I would tend to stick with the major brands that sell a lot into the US like the three above.
To keep this on topic for this thread we should say that in this device class you are typically replacing an existing downlight and again they are wired directly into the mains. You can usually adjust size within an inch or two by using a rim ring, which is why you will see them listed, for example, as two sizes for the same device.
Some are white only, but once you get to smart devices most of them are color adjustable or at least color temperature adjustable.
This is an expensive option for a room, so they are most popular either when you want color effects or when you want to create multiple lighting zones in an area which is all on the same circuit controlled by one switch. So you do see them, for example, in home theater rooms. And kitchens where you have separate work areas that you want to light more brightly.
The 5/6” size is the most popular and you will have the most choices with that, as you mentioned, but there are some made in other sizes like the 4 inch that you are looking for.
In the 5/6 inch size, Sylvania smart was the most popular that worked with smartthings for several years but then California passed a law on energy efficiency that those don’t meet, so they can no longer be shipped to California.
So that has now become another feature you have to look at in this device class: can they be shipped to California?