The Radiometer is an invention of the english physicist Crooks and show vividly the conversion of light into kinetic energy. The black surface of the solar wing – wheel (a circle of elements which are sensitive to light) absorbs much more light energy than the bright one. Because of the stronger heating of the air molecules on the black surfase a higher pressure arises there that leads to a rotary motion of the solar wings. This rotary motion is the result of the light incidence (radiometer is standing or hanging by the window) and as well as possible in the gleam of lightbulb inside a room (no cold neon light). The more intensive the light is the faster the solar wheel moves. As the rotary force on the solar wing-wheel must be higher than the resistance of the air molecules a partial vacuum is generated in the ball. This demonstration model of a physical process show how light is transformed into kinetic energy. Therefore the radiometer may be called a small solar power station.