Light wind is called “Radiometer” in German originally. It is a physical device showing men how light energy can be transferred into kinetic energy. It is made of a glass ball and 4 metal blades set on a pin. When there is light on the metal blades，This four sheets will begin to go round and round, The Stronger the light is, the faster the sheets circumrotate. Because it is driven by light and operating like a “wind”. So we called it “light wind”.