Light sensor placement

I am getting 2 Xiaomi Zigbee 3.0 light sensors. What I wanted to ask is where is the best place to put these as I am wondering if they are placed in the same room as the lights that get turned on, then the lights will change the "brightness/lux" reading and might turn them off again. Would the best place be to put them as far away from any lights as possible. I did order 2 so that I can average them.

You'll just need to play around with what is best for your situation.
I have all mine in the same room as the lights and have the triggers set based on the readings they give for that location. I've had to move them around to find the best spots to give accurate enough readings to trigger the automatons.
I use Motion lighting for all my automatons and don't know if it is just my hub but the turn off if lux is brighter than x never works so don't have an issue with that.

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Hi at9

Thanks for the info, I would also not mind if the turn off if lux is greater than does not work, as long as it turns on. I will try them in a few places then. I was wondering if I would need to put them outside somewhere but was not to keen in case of rain.

I use Philips Hue Outdoor Motion Sensors (averaged out) to get an outside lux reading.
(they are a bit expensive but to me, worth it - They do motion, lux and temperature)

This 'average' then changes my mode to evening (if low enough) so that my motion lights work (they are restricted by mode)

I also don't care if the lux rises a bit - I don't want my lights going on/off all the time


I've tried using outdoor lux levels as a mode trigger countless times over the years but nearly always ended up switching back to some sort of time based event.

What sort of average do you use? How do you account for dark / dull days and the position of the sun?

I was looking at graphs for my hue outdoor sensors to try and ascertain what level to use as a switch but the range of readings varies too much.

"Graph One" shows a typical bright and sunny day, you can see that if I average those readings from these four sensors it's going to be thrown high by the fact that the two sensors at the rear are catching more evening sun / light. Looking at logs shows that people started to turn on lights around 19:45 or so but at that time outside would still have been averaging a high value, probably over 5000 or so.

"Graph Two" shows a less bright day, although still reasonably sunny. You can see the sensors are more uniform here but if I'd used the trigger value from the previous graph then we'd have switched to evening mode far too early.

I suppose I could filter out extremes, or perhaps do some sort of fancy algorithm that tracks what sort of day it's been in terms of lows and highs. Pretty sure I've gone round in circles a load of times on that already and always end up coming back to simple "sunset" or time based / season events!

I use my Average All app to do the lux averaging between 3 outdoor hue sensors
(Two at the rear of the house and one at the front - My house is north/south with the rear facing south)

I use another one of my apps 'Modes Plus' which allows changing modes on lux levels with restrictions on the current mode and the proximity to sunset/sunrise

So for example..
My 'Evening' mode is triggered by an average lux level below 2000
BUT... it can only work if the current mode is 'Afternoon'
AND it is configured to work ONLY within 1 hour of sunset

So if the level goes below 2000 but the hub is in morning mode.. then it won't trigger
If it's already in afternoon mode and the lux goes below 2000 it will only trigger IF the time is after sunset - 60

It is easy enough to set the correct level to switch at by waiting to see how dark it should be before turning on your lights.. then just check the average level

This works well for me
I have been using this set up for almost 2 years (I just used to use weather underground for lux before I got the hue sensors which are MUCH more accurate)


Yeah so lux alone isn't much use unless it's also constrained by other input data :slight_smile:

Was hoping that you'd come up with some super intelligent formula for predictive lux level switching based on historic readings!

AI for lighting .... surely by now that should be a thing?

I think I will have a play around again, perhaps by determining a rolling 7-day average lux level for 15 minute time slots during the couple of hours before sunset. Then using that as the trigger level rather than a fixed value. Or maybe doing some sort of "rate" measurement, i.e. how quickly and how much the lux level is falling, so even if the current average is high if it's falling and falling fast then use that as a trigger.

The other way of doing it is to just record lux in individual rooms using the hue indoor sensors or similar.
That way you can just 'dampen' them a bit so that they don't keep changing on/off
Then use an average or say: 'if 3 of the room are dark enough for the lights, change to evening mode'
or some similar logic
easy enough to do, you just need to add the hardware and work out what levels you want to switch at

If that is a true indication of the 'about to be dark enough' level then that would also be easy enough to do.

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