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PaulEngh

Sensor reporting 0 lux even if there is more than enough light outside.

Question

I have the motion sensor report light intensity throughout the day, and use this info to control exterior and interior light.
 

The graph shows it reports various light throughout the day, but when the dark period starts it ends up reporting 0 lux even if there is more than enough light outside. 
 

Is there a way to calibrate the sensor?

I am based in Norway. 
 

The photo is shot at 23:53 last night using my iPhone 7

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Posted (edited)

parameter 40 is by default at 200lux, when you need measurments at low light levels, you will need to change to to lower value (e.g. 25-50lux) - but don't forget, this means all the time each every 25-50lux change will trigger report, which means battery will die after few months.

 

EDIT-  Fibaro itself does not recommend to set lower value than 50lux, not that this does not work, but simply to prevent people from crying about empty betteries.

Edited by tinman
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Posted (edited)
22 hours ago, tinman said:

parameter 40 is by default at 200lux, when you need measurments at low light levels, you will need to change to to lower value (e.g. 25-50lux) - but don't forget, this means all the time each every 25-50lux change will trigger report, which means battery will die after few months.

 

I have discussed this with Fibaro and they have accepted my "suggestion" to consider to try something different when they design their next generation sensor. Imho our eyes are more or less "logarithmic" and setting that parameter to 25 only partially solves the problem, and introduces another problem: if it sees sunlight, clouds will make it report "like crazy" while we usually are not interested in that level of detail. While still not getting a lot of data points in low light. See graph. Each dot represents a report of my first gen FGMS (fw 2.8)

 

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Edited by petergebruers
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  • The main issue here is the reported lux level drops too fast and it reports zero even if the outdoor light is still visible (see my photo above). 
     

    So by calibrating I am looking for a way to have it report more grained in the darkest periods of the evening. 

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    Posted (edited)
    22 minutes ago, PaulEngh said:

    So by calibrating I am looking for a way to have it report more grained in the darkest periods of the evening.

    There is no such thing as "calibration" on this sensor. The only thing you can do is lower parameter 40 and lower wake up interval... But if it reports 0 when you think it should report something then I don't know how to improve that. I guess your main issue is this: you are pointing this sensor downwards, to detect motion. But by doing so you measure the light reflected from the ground. You could get better results if you pointed it upwards, but then you no longer have a "motion sensor"...

     

    Are you a DIY person? Make your own sensor based on Z-Uno!

     

    Or wait until Fibaro implements Zigbee + support for a dedicated light sensor like the Zigbee  Mija Illuminance sensor GZCGQ01LM

     

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    I have to test it thorough but my first tests showed me it has a good range (EDIT: though iirc it has 1 Lux precision so you won't be able to go below that!).

     

    I am not sure if the "Neo" Motion sensor would work any better, I only use mine indoor and I can live with a 25 Lux threshold...

     

    I'e been on this forum for > 5 years and you are the first one to complain about the accuracy of low light measurements. It also annoyed me when I bought my first sensor, that one did not even reported in Lux :D

     

    So now we have 2 people (you and me) worrying about Lux levels < 10 - you are my friend! ;)

     

    Do you have any other sensor to compare with?

     

     

    Edited by petergebruers

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  • Posted (edited)

    I have other sensors which is not Fibaro. They are in other locations. 
     

    Thing is This is outside. And I do not need motion sensing. Will it work when exposed to rain And snow?

     

    is the casing waterproof?

    This photo is taken 23:50 tonight. Even at autoexposure we can clearly see it is not 0 lux outside. 

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    Edited by PaulEngh

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    Posted (edited)
    18 hours ago, PaulEngh said:

    Thing is This is outside. And I do not need motion sensing. Will it work when exposed to rain And snow?

    No and no, and on top of that they are specified for operating between 0 and 40 °C and you are in Norway so probably go below -10 °C? I have such a sensor under a roof like yours and my sensor is still OK after 3 years but that might be "pure luck", it is definitely not water proof.

     

    18 hours ago, PaulEngh said:

    This photo is taken 23:50 tonight. Even at autoexposure we can clearly see it is not 0 lux outside. 

    I cannot judge "Lux" from a photo, You are closer to the North pole so I guess it is not "0" but remember, the sensor is looking at whatever is below - so what surface does it see? If it is very dark, it might register < 1 Lux indeed. It is essentially "a one pixel camera".

     

    I have a cheap Luxmeter UNI-T UT381 for that, purpose, bought it years ago from a local supplier and cost me about 50-60 EUR ;)

     

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    If you buy one, you will notice none of the available sensor matches your UT381  because it depends on the "angle of view" and orientation of the sensor (and possibly even more factors).

    Edited by petergebruers

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  • I’m giving this approach a shot tonight. 
     

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    Posted (edited)
    On 6/18/2020 at 3:18 PM, PaulEngh said:

    I’m giving this approach a shot tonight. 

    Interesting experiment! I have been busy so haven't tried anything yet but your question "kept nagging at me" so to speak. I have a BH1740 sensor made by Rohm somewhere, I am the author  of a scene to use this device on a Z-Uno:

     

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    Incidentally, that sensor is also supported by  tasmota:

     

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    But I am not sure if that would help because I wrote this comment when I published that sketch: "Reports 0 - 78642 Lux. Resolution: 1.2 Lux" and the spec sheet mentions a lowest value of 1 Lux...

     

    I have been thinking that what you define as "Dark Outside" means "too dark to orient yourself" and I estimate the Lux level for that to be somewhere between 0.5 and 5 Lux, probably towards the lower end of that range... the orientation of the sensor matters because our brain pieces together visual clues from different images (angles) which a sensor cannot do.

     

    I may have a different sensor with a wider range and I might buy a TSL2591 but it is quite expensive compared with BH1750.

     

    I also have LDR (CdS  cells, which are severely restricted in Europe because of ROHS but it is not illegal to own them 😀)...

     

    So if you or someone else on this forum enjoys tinkering...

     

     

    Edited by petergebruers

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    I just remembered... I think I have a MAX44009 module.. The spec sheet mentions it has max dark current of 0.05 Lux and plenty of resolution.

     

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    You can buy breakout boards on the internet but I doubt they are genuine, reputable sellers say this component is obsolete, so not a clue about performance ;)

     

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