SPARKFUN TRIAD SENSOR VALUES MEANING

Sensors Imaging
1

Hello,

This might be a silly question, but I am trying to measure different parts of the human body (finger, ear, wrist, etc.), to determine the levels of a substance with known wavelength. So, in my case, I am taking measurements from channels K and L. But, the question is, what is their value mean? Is it the absorbance or the reflectance? and this value is Hz?

2

Hello,

As per the [datasheet, the units of those channels are counts/(μW/cm2). These channels measure a sort of intensity of light at a specific wavelength. You can measure an object in either absorbancy or reflectivity, it depends on how you’re using the data.](https://cdn.sparkfun.com/assets/c/2/9/0/a/AS7265x_Datasheet.pdf)

3

This is the level of light entering the sensor, so if you are turning on the LED and then measuring the reflectance, it is how much of each wavelength is reflected off the surface. To make sense of this value though you need to also know the intensity of the wavelengths hitting the surface so in practice a piece of white dispersing material like styrofoam is measured first and is taking as a reference value. Then you take the measured value of the sample (i.e. the finger, wrist) and divide that by the values from the white styrofoam to get the reflectance values. If you use just the raw value it will look like a mess because the white LED has a rough spectrum profile, but the reflectance values normalized to white styrofoam look much more sensible.

4

TS-Brandon:
Hello,

As per the [datasheet, the units of those channels are counts/(μW/cm2). These channels measure a sort of intensity of light at a specific wavelength. You can measure an object in either absorbancy or reflectivity, it depends on how you’re using the data.
[/quote]

Hello, I succesfully run the sensor but I would like to ask if I can use the AS7265x sensor to measure water samples because I want to measure its absorbance and transmittance but i dont know how to interpret or convert all the resulting data.](https://cdn.sparkfun.com/assets/c/2/9/0/a/AS7265x_Datasheet.pdf)

5

If you want to measure absorbance of substances dissolved or suspended in water, then a two step process is required. You will need a white light source and sample holder in a fixed arrangement.

First, record the 18 sensor values for pure water in the sample holder, then record another set of 18 values for the water sample of interest. Take the difference of the logarithms of those values to get the 18 values of absorbance. Or, you can take the logarithms of the 18 ratios.

Tutorial: https://www.bmglabtech.com/absorbance/