Measuring Sunlight
You can measure the duration and the intensity of sunlight using a simple glass sphere device called a Campbell-Stokes sunshine recorder.

Burning a Trace
These focus light from the sun onto a piece of card where it leaves a burnt trace if the sun is bright enough. The more sunshine there is, the longer the line. The sphere acts like a magnifying glass and the card has to be specially treated so that it won't catch fire.