I’m using the Qwiic UV sensor based on the AS7331. The arduino code is great but I don’t understand the units or how they are calculated. When I point it at the sun on a march sunny day, I read:
UVA = 7410.94
UVB = 53.16
UVC = 29.83
What are the units for these numbers?
Since the chip has max ratings that are kind of similar for the 3 spectral regions, I’m surprised that they’re not similar numbers. They differ by 100x. Is that expected?
What are the units for these numbers?
µW/cm2
Since the chip has max ratings that are kind of similar for the 3 spectral regions, I’m surprised that they’re not similar numbers.
Where did you see this?
For an estimate of the power density in the UVA, B and C spectral regions, due to solar radiation arriving at the Earth’s surface, it is helpful to study the spectrum of solar irradiance. Notice the steep falloff at the high energy (short wavelength) end of the spectrum.
UVA (315-400 nm) UVB (280-315 nm) UVC (100-280 nm).
Excellent graph!
I should have credited the Wikipedia article for that graph:
YellowDog:
What are the units for these numbers?
µW/cm2
Since the chip has max ratings that are kind of similar for the 3 spectral regions, I’m surprised that they’re not similar numbers.
Where did you see this?
The max ratings are from the data sheet (“Full scale range of detectable irradience”). The curve is vaguely helpful but it’s hard to say from that if the UVC should be 10x, 100x or 1000x lower than the UVA. I wish there were some way to independently verify what I’m seeing. I’ve spent a lot of time looking for other example uv readings, but they are all very steep curves that would be hard to integrate with any accuracy. Or they are already combined into the UV index.
I kind of understand the data sheet but I get a bit lost with the code.
The UV index is an extremely crude measurement, intended to be only a very rough guide as to exposure. If you read up on how the index is actually estimated, you will see that the effort to obtain “accurate” UV index values is rather pointless.
