It is a well know effect, but I just wanted to check my self. Here is a graph of UV. It’s pretty constant except for two spikes. Those were the moments I hold a piece of A5-sized white paper next to the unit. Confirming that partly clouded weather can have elevated UV values.
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That’s probably why I get sunburnt while it’s cloudy and windy lol
Did you hold the piece of paper from the side or over the top?
vertically, from the side. Horizontally, over the top it would probably decrease the measurements. If you were to hold it at an angle at some point it might increase the values.
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I see interesting. I thought because it was in the middle it wouldn’t capture light from the sides. Now I can see your point about painting the spikes on the Bird Deterrent bright white.
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This is an interesting experiment. I am not sure I have all of the knowledge I need to come up with a good conclusiion, but, I am struggling with the concept of using a sheet of white paper as an analog for clouds. White paper, from what I am reading, is pretty good at reflecting UV radiation, and I am thinking most of what you are seeing is due to that reflection. Cloud physics are a lot more compicated than just light reflections. Clouds absorb and re-radiate energy (often at a different wavelength), as well as some reflection of the energy, and thinner clouds may generally allow the radiation to pass thorough mostly unimpeded (except, since you can see them, they are reflecting/radiating at least some long wave radiation). I have been trying to find some references for this kind of experiment but I have not found any. Do you have any references for this kind of experiment?
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just some very quick googling:
“in 2004 Australian researchers reported that the UV-B rays associated with DNA damage were up to 40% stronger under partly cloudy skies.” (a pretty non-scientific source https://zidbits.com/2011/04/on-cloudy-days-are-uv-rays-stronger/)
For a more scientific article https://uvb.nrel.colostate.edu/UVB/publications/asos_grant.pdf (which i didn’t read this time)
Of course that is using real clouds, mine was just an experiment.
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Thanks. I will read the paper. I guess I was/am struggling with the assertion “Confirming that partly clouded weather can have elevated UV values.”. I don’t think that using a surface that is very good at reflecting UV radiation, and, assuming that what you are measuring is that reflection, actually confirms that. Certainly a fun experiment, but, I am not ready to reach that conclusion.
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I like your critical look! Apparently a big part of the UV increase is related to just that… reflection of clouds. But there is more to it, so it can increase even more. My experiment only kind of confirmed the reflective part without any further quantization.
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