The issue is, sensors are not equally responsive to all wavelengths. The efficiency of a sensor at collecting light is quantum efficiency - an ideal sensor makes 1 electron per photon. However, a real sensor does not, and for example in green there might be 0.5 electrons per photon, in red 0.3 and in blue 0.2 (pulling random numbers just to illustrate).
For professional spectrometers, this is calibrated (they either have a built-in self-calibration function, or you gotta calibrate them with calibrated external lamps).
I do not have such a light, so I do not know how my spectrum really looks like. Might be that green is too high compared to red and blue, might be it is too low (very simplified, in reality the spectral respone of the sensor can have all kinds of dips and peaks and other weird shapes). Since DUV, CRI, R9 and even CCT depend only on the shape of the spectrum, if that shape is off, so are all your results. That’s why it needs to be calibrated, and I have yet to figure out how to do so.
The spectral response function of most monochrome CMOS sensors is pretty wild, here an example (source: https://www.researchgate.net/figure/Spectral-response-of-the-CMOS-sensor_fig12_2977754):
Getting a useful spectrum out of such a sensor without previous calibration is pretty much impossible.
The v0.3 seems to be kinda pre-calibrated (against a “sunlike” lightbulb and a commercial spectrometer), but the results I measure still look off compared to what I’d expect - my LEDs have a green peak they should not have. Maybe there is significant variation between multiple little garden spectrometers.
XHP70.3 HI 4000K R70, reference measurement taken by @koef3 with a professional spectrometer (full review and report here: LED test / review - Cree XLamp XHP70.3 HI N4 color kit 5D (≈ 4000 K, 70 CRI) - domeless performance even at 20 A!):
XHP70.3 HI 4000K R70, measurement from my Little Garden (v0.3 software, CCT/CRI evaluation performed with a free but closed source Osram software):
The dips at 520/590nm and the peak at 560/570nm should not be this pronounced, imo. The waveform at 460nm also looks off compared to what koef3 measured.
But I think we are getting too deep into offtopic - sorry steve! I will make a thread for the Little Garden these days when I find time, and show my results and experiences there, so we stop spamming the Opple thread with unrelated stuff.