I’m not sure if this is the right forum but I’m rather disappointed with the quality of the ISL29125 RGB sensor. The red sensor performs fine but the blue and green sensors always show almost the exact same reading. That is, if I shine blue light on the sensor, the blue and green sensor readings show almost exactly the same number, and if I shine green light on the sensor, the blue and green sensor readings again show almost exactly the same number. I tested three units and all three exhibited this same problem. Am I the only one to notice this issue?
Hi, thanks for writing in.
I cannot say that I have seen multiple units demonstrate this issue before. I feel like perhaps if you tired changing your light source you may get different results. Could you try?
I look forward to seeing the results.
Yes, you are right, thank you. I was using an RGB LED as the light source. When I instead use discrete LED’s the sensor’s differentiation between blue and green is better, indicating that the spectrum of the discrete LED’s must be different than the spectrum of the RGB LED. Still, though, to my eye, with the RGB LED that I was using at first, the blue appears purely blue and the green appears purely green. I expected the ISL29125 sensor to agree with my eye, and it definitely doesn’t.
Hey again.
Interesting. I am not proficient enough with the technology to argue exactly what is going on here. It seems like the product may not meet the needs of your application.
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Off hand, it sounds to me like the so-called “RGB” LED isn’t truely RGB. Maybe it’s generating green by mixing blue and yellow… only way to tell for sure would be a spectrometer or spectroscope, though if you’ve got a triangular prism, passing light from the LED through it and examining it with your eye would probably reveal what colors it’s actually generating. (50 years ago when I was in high school, a spectroscope was a standard feature of high school physics labs. Astronomers are also fond of using them, so if you can find an astronomy club nearby, odds are one or more members would have a way to do spectral analysis on the “RGB” LED, if you want to go to that much trouble.)
Ah, sounds similar to Newton’s Prism. I don’t have access to prisms, personally. Seems like a fun experiment to conduct, though.
Yeah, I think you are on the right track. Chances are perhaps that the LED is not producing true colors as advertised. Seems logical to me.
Thanks for the post!
American Science & Surplus https://www.sciplus.com/ has several that are under $15. (Use their search for prism) Also, you might wander through a thrift store – any transparent thing in the shape of a prism would do – they often are used to decorate chandeliers, or as Christmas tree decorations. Diffraction gratings will also work (actually that’s what astronomers and often physicists use rather than prisms), though I haven’t seen any advertised at reasonable prices in several years, though I haven’t been paying much attention. A green “gel” filter (like used in front of theater lights) should also answer the question – if the LED is “tricking the eye” by combining, say blue and yellow, very little should get past a truely green filter.