Zigbee / Matter Motion Switch | Project Linus (Blue Series)

We definitely don’t need precise lux readings (they won’t be precise anyway, it’s probably easiest to aim for arbitrary units) but it would be really nice to at least get out something more precise than 1-10. Bins that small won’t let people adjust the finer end of the scale to match their actual lighting.

I’d suggest exposing a value that goes 1-256, do the log-scaling in software on the switch so those values are at least ballpark linear to the human eye. This will be much easier for most people to understand and work with than a 2048 count log-scale value.

When selecting sensors, aim for more resolution in the low end of the scale - the difference of a couple lux will matter a lot for some people’s “the lights are off, or very nearly off” automations, where nobody really cares at all about the difference between cloudy and direct sunlight. If the max on the sensor is 500 lux, you’ll save a lot more of the scale for the low light situations where precise control matters.

As far as use cases - my existing motion sensors offer brightness that I can use to help decide “should this light come on, and how much”, this would do similarly. It’s possible to use the various automation frameworks to say “ok, of the 12 lightbulbs nearby, which ones are on, and what does that mean about whether this one should come on?” but that’s a huge pain. It’s much easier to say “it’s dark, so we’ll turn on the lights when someone comes into the room.” The tricky thing is understanding what “it’s dark” means contextually.

  1. A Lux sensor would help me round out my home automation with less upkeep. Cloudy days my house gets darker than usual, thus an automation around “timing of sunset” isn’t always accurate. Being able to kick off/on lights using lux readings versus scheduling would be more accurate and a lot less upkeep from creating routine etc.

  2. For me, accuracy would only need to be accurate enough to tell when a room is dark/light, but would need some accuracy of how to distinguish “cloudy” dark from “night dark”.

Another thought with the lux sensor is how you report those values. I think this was already discussed, but here are some visuals to help people understand. If you use a linear scale, big changes in lux at the brighter levels aren’t very noticeable to the human eye, but changes at the low end are.

Linear scale plot:

Log scale plot:

The change in lux during ramp up in the morning from 6:30am to 9am is a very small fraction (maybe 10%) of the max lux if you plot it linearly, but if you do the log plot now that change is 70% of the total. So you are able to capture a LOT more granularity at the dim levels, which is where you need it.

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I also would like to have precise low lux but don’t care after,
I wanna know the difference between total dark and low light, for instance, when you wake up at night you need almost no light just to navigate the corridor so you need to know that is not actual dark but just enough light if that make sense.
the log idea seem very good

Will it be possible to know thee distance between the person and the sensor ?