Hello Saurabh
I guess there are a few challenges
The first is how you measure the LED intensity with the spectrometer. In practice the spectrometer is at 90 degrees to the LED path so you only get a particularly good signal if there is something in the way (i.e. a test tube with media/cells) to scatter light into the spectrometer. Otherwise, what you are measuring is somehow the random internal reflections in the device which may be very sensitive to geometry. What I’d reocmmend is making some cloudy solution as your standard “scatterer” and then using this in all reactors.
Second, yes, there are sources of variability in both the LED output and the spectrometer. Probably the largest amount of this comes from small changes in alignment made during assembly when the lens is glued to the LED and the spectrometer is soldered in place. There is also variability in the individual LED emitters and spectrometer, which are off the shelf parts so there is nothing we can really do about this. We try tocalibrate this variation out for fluorescence measurements by doing the ratiometric measurement as you stated, but in your case you need a constant ABSOLUTE amount of light. I’d start by doing the above (standard scattering solution) and seeing how different it is, but if the answer is still “not good enough” then ultimately what you may need is to buy an off-the-shelf light meter that can be inserted into the top of the device so you can have a consistent measurement across reactors. This way you will know exactly the light output and have the same sensor for each (i.e. not using potentially variable AS7341 chips) to have the best possible calibration. You can get cheap light meters for <100 USD usually which are probably more than good enough to do the trick.
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