My wife, Amy, has done a fairly good job of convincing our daughter to wear sunscreen, at least when the sun is shining and the temperatures are soaring.
Amy also does a fairly good job of convincing her to wear sunscreen on cloudy summer days, arguing that just because you can't see the sun directly doesn't mean the rays cannot reach you.
But as North Carolina's weather has cooled down, my daughter is far more reluctant to protect her skin. "It's not hot outside!" she protests. Of course, we know that UV radiation is independent of air temperature, but that's incomprehensible to her, especially because both the air and the UV radiation are effectively invisible. So when we were shopping at REI this past weekend, I had to buy an Oregon Scientific UV Monitor.
As soon as we were safely outside, I popped in the battery (included) and took a reading of the noon-time sun: it registered 10/High and told me that the safe exposure time for skin type 1 was 14 minutes. Thankfully, I'm more like skin type 2 (sometimes tans; usually burns) rather than 1 (never tans; always burns). But in our house, skin safety is important, so it's good to know the worst-case scenario.
Speaking of healthy things I do, I walk to lunch almost every day. The walk is about 15 to 20 minutes in each direction. Amy tells me I should wear sunscreen, but I think the walk is short enough I don't need to. I took the meter with me on my way to lunch to settle the matter.
The monitor has a timer function that can be updated so one can measure and update one's exposure as clouds move in and out of the scene or as one walks under the shade of trees. With no sunscreen I left the SPF setting at its default of 1. I set out for my walk and registered UV ratings between 10 and 2. By the time I got to lunch, I'd used about 70 percent of my average exposure budget.
Fortunately, on the way back, it was cloudier, and my budget expanded as I walked briskly back. With about 500 yards to go, the sun came out strong, for good, and I took yet another reading: 10/High. Suddenly I had only two minutes left on the clock. Was it 2:59 or 2:00? The walk was downhill. I ran the 800 competitively in high school. Could I stretch it out and make it to the shade before the timer went off?
Alas, with 20 yards to go, the timer told me I had exhausted my budget. Amy was right. I guess I do need to bring sunscreen to work, even in autumn.