As have some other people, my Atlas has been reporting low UV readings. I did a little experimenting, and so far what I have is looking promising enough.
Let me start out with, to do this, you are more than likely going to ruin the diffuser (mine was), so proceed with caution. Also, I live in Phoenix, AZ so we get a LOT of sunshine with high UV.
My thought was that the diffuser wasn't letting enough light through, causing UV to report too low. I removed the light sensor from Atlas and removed the diffuser (with the little black ring). I peeled off the diffuser. It was really stuck on the black ring, so while removing it, it completely tore to pieces (making it unusable if this procedure failed). Also, the black ring tore in one spot, but I still made it work.
I simply cut a circle, the same size as the diffuser, out of parchment paper. The paper wasn't completely clear, but I could see beforehand that it would let more light pass through than the stock diffuser would. I placed this "new diffuser" in the housing, fit the black ring back in to secure it, and put everything back together.
The result? While not necessarily perfect, it is definitely better. When I did this 2 days ago, UV was supposed to be around 9. Normally on a day like this (such as previous days with the same UV forecast) I would only solidly get to a 4 (maybe a reading or two might touch 5...but rarely). After using this new diffuser I solidly hit 7. Much better than the previous 4's that I had been seeing.
This was 2 days ago, so yesterday I thought I'd see if I could make it better. I searched around the house to see what I could find that might let even more light pass through. I found some scotch tape (the type that is a bit "cloudy", not perfectly clear). Visually I compared it to the parchment paper and it did seem like it would let maybe a little more light pass through. So I did the same procedure as I did with the parchment paper, and the results were not good. I had readings go as high as 13, and then drop very low (a couple times hitting a one), and then shoot right back up again. I took Atlas apart again, but this time using the same tape, I made it double thick (thinking this might filter a bit more light and stabilize the readings). Nope, same readings were occurring...extremely high with extreme bounces in UV levels.
My next attempt, I used a different kind of tape that seemed like it would filter more light than the first tape that I tried. Same result. Super high readings with wild fluctuations. Even tried making this tape double thick, and the same results occurred. I'm not sure what may be unique about tape (compared to the parchment paper) that would cause this to happen, but those were simply the results that I got.
By the time I got done with this new round of testing with the different tapes, it was about 2pm. I put the parchment paper diffuser back in, and right away my readings got more in line where it should be, and without the wild bounces. While by the time I got the parchment paper filter back in, it wasn't solar noon, so I'm not sure yet what the readings will be. But I anticipate that they will be today at least similar to what I had the first day I used the parchment paper diffuser.
We're only supposed to hit a UV of about 8 today (a bit of cloud cover), so I'm gonna keep my eye on it and see how it responds. The next few days are going to be sunny with a forecast of UV in the 9-10 range. So I'll have to see how close this gets.
If it is supposed to be a 9, a reading of 7 is acceptable to me. A 4 is not acceptable. So hopefully this will make Atlas a lot more accurate. How accurate will it be this summer when our UV gets extremely high? Only time will tell. But as long as it can get close, I will be happy.
So, there ya go. A possible fix for low UV. Proceed at your own risk.
Peace!
