I recently bought the Sparkfun Triad Spectroscopy Sensor - AS7265x. I am testing out the possibilities with the sensors on this chip. I noticed the provided datasheets for the light sources, which got me interested in calculating the expected values. Here I ran into a few problems and I hope someone can help me with them.

NIR and UV light source intensities are stated in mW/sr which is very helpful, although I presume the distance is somewhat of importance. I’ve found the formula for the solid angle to help determine the expected radiant intensity on a distance, because the formula for radiant intensity is I = P/A which in terms of units is [W/m^2] = [W] / [m^2]. Although with the IR and UV led the radiant intensity is given in mW/sr. Therefore I multiplied the [mW/sr] with [sr] and replaced [W] and replaced [m^2] with [cm^2] in order to obtain [mW/cm^2] which I can work with. The steps surely must sound vague, so ask away for clarification.

By using this formula and the given information I was able to calculate the expected values. I took in account the amps and wavelength for a different intensity, but my values still are lower then the device gives me. For example on the IR led on 860nm I have calculated 195 uW/cm^2 and my results give back roughly 19200 uW/cm^2. My measuring setup is not nearly perfect, but these values are extremely different. However on 900nm I should have lower values (because of the lower intensities the datasheet describe) and the results are roughly 1950 uW/cm^2. I wonder if I have messed up my calculations or if the sensor does something very unpredictable. It seems consistent in measurements, but it responds so much heavier to UV and IR compared to visible light.

Also, I’ve noticed the datasheet says the sensors are calibrated to reflective surfaces. Does that mean it is impossible to get accurate results with direct exposure to light? (I bought the LEDs and installed them a certain distance from the sensor.)

I’d be super helpful if anyone could give me more answers. It would also be okay to point me into the right direction. Feel free to ask for more clarification.