I found this forum on Google. This may not be the right section so excuse me if so. I have a rather simple question though. When you take a magnifying glass on a sunny day and position it just right over a piece of paper, the paper will start to burn. Is the inverse square law (distance) the biggest factor at play in getting the paper to burn? Or is it more that due to the way the lens is positioned, it concentrates the light into a single point rather than diffuse it?