Grove Light Sensor - conversion to lux


#1

Hello,
I am reading from the analog light sensor, and I get values between 500 and 700 or so.
But, what are these values? How do I convert these to lumen or lux?
Thanks!


#2

Hi @LuCavallin,

That’s a really good question.


I’ve read more on this sensor and I found out that the light sensor's model is GL5528.
Its datasheet can be found here:

So, by going over the datasheet, you may find some interesting bits of information. Especially on page 2.

What you need from this datasheet is a plot between the light sensor’s resistance and the amount of lux - take a look in the datasheet.
After you get the graph, we then need to interpret it in order to get a formula - this thing can take a lot of time.

Unfortunately, the datasheet doesn’t seem to be really informative - it’s quite hard to decipher it.

You may want to take a look on this forum - these guys are also struggling with this sensor in particular and their solution may be worth something:


Then, I’ve looked over the Grove Light Sensor's schematics and I saw the following:

Let’s say we find out a correlation between the lux and the output voltage of the light sensor.
But there’s another impediment we have: it’s the amplifier we have there. We’re not sure what are the amplifier's settings.
Again, we would need to calculate (physics involved too) in order to reach a correlation between the lux and the Grove Light Sensor's output voltage. And this thing can be prone to human errors as-well.

Anyway, here’s the amplifier's datasheet:

The good thing about this datasheet (which comes from TI) is that it’s a lot more explicative.


Personally, I think you have 2 alternatives which sound a lot better:

  1. Use a professional light sensor in order to calibrate this Grove Light Sensor. For each reading, you would find out the ratio between the lux and the analogRead value from the GrovePi.
    The bad thing about this method is that you need to take lots of measurements (tens of them) in order to get a somewhat precise sensor - that’s because the sensor’s resistance isn’t proportional to the amount of lux.

  2. Use another Light Sensor that’s made for measuring the lux - it needs to have a Grove connector. We currently don’t have another sensor in our catalog that suits this need, but Seeed has one.
    The following sensor is compatible with our GrovePi platform.
    Here’s a link to it: https://www.seeedstudio.com/Grove-Luminance-Sensor-p-1941.html


Please let me know what decision you further want to take and if there’re any more questions, Luca, please bring them on to me.

Thank you!