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Posts: 2
Registered: ‎09-12-2017

Si1133 UV, LUX calculation

I'm currently working on Si1133. I used this code :

 

https://siliconlabs.github.io/Gecko_SDK_Doc/efm32g/html/si1133_8c_source.html

 

Can anyone tell me more about functions SI1133_calcPolyInner and SI1133_calcEvalPoly? Also, when i run the sensor in forced mode, indoor, for lux I get value somewhere around 1000-1200, and when i turn off the light it goes down. But, for uv value i get really low values, order of e-3, e-4, but sometimes it shows 4000. I would be thankful if someone tells me is that ok, and if it's not how to get the right uv index.

Posts: 97
Registered: ‎04-09-2015

Re: Si1133 UV, LUX calculation

Hi,

 

Those 2 functions implement the polynomial equation to calculate UV index and LUX value in fixed point format. You can either follow the example code or use the floating point calculation if your system supports that.

 

Indoor UV index level is normally 0. If you see some abnormal result (i.e. 4000), that's because the sensor is completely exposed to the light without any optical design. The light coming in from the side of the sensor can affect the reading. You can put a rubber ring around the sensor to avoid those issues.

 

Regards,

Tony

Posts: 2
Registered: ‎09-12-2017

Re: Si1133 UV, LUX calculation

Thank you for a quick response!

 

Can you tell me where I can find floating point calculation for UV and LUX? 

 

Sincerely,

Vule

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Posts: 97
Registered: ‎04-09-2015

Re: Si1133 UV, LUX calculation

You can find the UV index calculation formula in the UV application note:

https://www.silabs.com/documents/public/application-notes/AN968-Si1133-UV-Index-Sensor-Electrical-an...

 

We do not provide that for LUX calculation because that's too complicated.

 

Regards,

Tony