You may also find out that your MVB does not need to be replaced depending on what the meter says. Reading this thread has sparked my curiosity. Over the weekend I will check the UV levels throughout the day if I can. I live in South Eastern Washington state so I'm a little more south than you are but not that much more. My Russian tortoise spends got to figure all summer outside, June through August 24/7. And then during the day for at least a couple hours a few other months.