<p>I am trying to create a homemade Sky Quality Meter (SQM) using a TSL2591 light sensor. This sensor measures Illumination (lux), but SQMs measure Luminance (mpsas). I have seen that there are many projects doing something similar, but each one uses a different conversion, which I don't understand.</p>
<p>Is there a way to do this, or to get a good approximation? Note that I am not a physicist, I am a simple developer so all this is new and unknown to me.</p>
<p>Thanks in advance!</p>
<p>Sensor info: <a href="https://www.adafruit.com/product/1980" rel="nofollow noreferrer">https://www.adafruit.com/product/1980</a></p>

CC BY-SA 4.0
2022-02-17T10:16:32.140Z
Can you explain what “SQM” means?
Peter Erwin
CC BY-SA 4.0
2022-02-17T10:37:45.767Z
@PeterErwin "Sky Quality Meter", a device for measuring sky brightness. See this one for example: [link](http://www.unihedron.com/projects/darksky/)
Boube
CC BY-SA 4.0
2022-02-17T22:02:39.250Z
@PeterErwin [What would go into the design of a simple sky quality meter, used to measure night sky brightness?](https://astronomy.stackexchange.com/q/27305/7982)
uhoh
CC BY-SA 4.0
2022-02-19T06:10:20.733Z
I think what you really want is to convert the lux to magnitude, and divide that by the field of view of the sensor, to convert to magnitude per square arcsec.  And that's the measure of light pollution which you could convert to a Bortle Scale value.
Greg Miller
<light><photometry><luminosity><light-pollution>
DIY Sky Quality Meter: Conversion between Illuminance and Luminance
Boube
# DIY Sky Quality Meter: Conversion between Illuminance and Luminance

(Asked by: username_0 on 2022-02-17)

I am trying to create a homemade Sky Quality Meter (SQM) using a TSL2591 light sensor. This sensor measures Illumination (lux), but SQMs measure Luminance (mpsas). I have seen that there are many projects doing something similar, but each one uses a different conversion, which I don't understand.

Is there a way to do this, or to get a good approximation? Note that I am not a physicist, I am a simple developer so all this is new and unknown to me.

Thanks in advance!

Sensor info: <https://www.adafruit.com/product/1980>

**Tags:** light, photometry, luminosity, light-pollution
> **Comments:**
> **username_1**: Can you explain what “SQM” means?  
> **username_0**: @PeterErwin "Sky Quality Meter", a device for measuring sky brightness. See this one for example: [link](http://www.unihedron.com/projects/darksky/)  
> **username_2**: @PeterErwin [What would go into the design of a simple sky quality meter, used to measure night sky brightness?](https://astronomy.stackexchange.com/q/27305/7982)  
> **username_3**: I think what you really want is to convert the lux to magnitude, and divide that by the field of view of the sensor, to convert to magnitude per square arcsec.  And that's the measure of light pollution which you could convert to a Bortle Scale value.  

---

## 0 answers

