Ultraviolet UVA and UVB Light Meter, Display UV Index, UVA, UVB, and UVA+UVB Radiation Intensity, UV Light Tester, 240-320nm, 320-395 nm

I have two of these meters. One is UVB only and other is UVA/UVB. I tested them both with a Sperti UVB light at about 3 ft and they do not read even close to same for UVB readings.

Update:The company sent me a new meter for free that seems to have accurate UVI values, as I think they changed the programming of their meters after I emailed them about the problem (the previous meter had UVI readings that were way off). With the new meter, the UVI reading seems high, but I don’t know of any easy way to the accuracy of UVI except pretty roughly. The readings are a lot higher than the UVI listed on weather websites, but it could be the weather websites’ fault, as I don’t know how they come up with their UVI values. Also the ozone layer is becoming depleted due to the increasing number of recent manmade inventions that contain ozone-depleting substances (ODS) so more UVB and UVC rays are coming through the atmosphere and reaching ground level, and these wavelengths are almost entirely responsible for the UVI as compared to UVA.Previous review:The device works and the UVB reading (and possibly UVA) seems to make sense and to be accurate based on my analysis (the calculated UV index value matches the online weather report for the UV index for my city, giving about 7.4 vs 7.2 UVI). You have to ignore the UV index reading that the device shows (mine is off by very roughly a factor of 8—must be incorrectly programmed) and just use a simple calculation to get the UV index from the device’s displayed UVB reading: just use UV index = 0.01556*displayed_UVB_reading. This comes from the mckinlay-diffey erythema action spectrum equation to calculate the UV index, using the middle value of UVB in between 298 and 328nm (313nm), so this equation is (1/25)*10*UVB_reading*10^(0.094*(298-313)) or 0.01556*displayed_UVB_reading (ignoring the value for the UVA reading as it contributes almost nothing to the UV index equation). I’m just making a table to tape on the back of the device (actually I will use a fancy label maker that is like a sturdier, waterproof sticker) so I can just quickly read the UVB reading to see what the UV index is:UV index / UVB reading:0.5 321 642 1283 1924 2575 3216 3857 4498 5149 57810 64211 70612 771Also they do say they are working on fixing this issue on the displayed UV index on their device.EDIT: I measured and then calculated a super high UV index of 14 at midday, way higher than the weather report of 9.5. I think this is because the Diffey-Mckinley equation in the paper I read is only for between 298 to 328nm, and the wavelengths that reach earth’s ground level through the atmosphere in early morning would only be longer wavelengths, so the equation would be accurate for early morning because only wavelengths longer than 298nm would reach the meter and would show up as the UVB reading on the meter for use in the equation (the meter would only pick up 298 to 328nm wavelengths in early morning, thus matching the equation). But around midday, wavelengths shorter than 298nm would reach the meter (even if they are not high-energy UVC rays, perhaps even weak UVC rays a bit shorter than 298nm would greatly affect the UV index and would make the Diffey-Mckinley equation inaccurate), so the equation would be inaccurate around solar noon/midday. But I would have to take readings every hour on a clear day to test this hypothesis.I don’t know if the meter would be able to calculate even roughly what the UV index would be around midday (but the meter may be accurate for early-and-mid morning/evening), as I don’t think the meter knows how much of each wavelength is present within its spectral response range for UVB. Google generically says UVC is 100 to 280, UVB is 280 to 315, UVA is 315 to 400. Also I looked at the spectral response graph on Amazon for UVB for this product, and it goes from like 240 to 320nm, so I guess the device is measuring UVC and UVB in the UVB reading.It was and is set to 1.00 calibration factor. The sensor bounces between values of 3 and 20 for UVB when covered.I think that to accurately measure UVI I would need what the company here says is a spectral analyzer, which I guess tells you how much of each wavelength is present at every point in time and can integrate them.