I was flying along the other day in my Sport Cub when I became aware of a burning sensation just above my left knee -- I mean it felt HOT! I looked down and realized that the lens-shaped fresh air vent in the skylight was acting like a magnifying glass to focus the sunlight on my leg, and the heat went right through the pant leg. I draped a chart over my leg the rest of the trip. I may fashion a cloth plug to fit in the inside lip of the vent.

This photo doesn't show how the brightest, hottest light was pinpointed in the center of the bright area: