Classic experiment of heat creating motion.

• Ideal for classroom demonstrations of electromagnetic radiation
• Glass bulb with much of the air removed; low-friction spindle inside holds a rotor with 4 vanes
• When exposed to light, the vanes turn due to differential heating

Radiometer made from a glass bulb, from which much of the air has been removed. Inside the bulb, on a low-friction spindle, is a rotor with four vanes. Each vane has one black side and one silver side; one black vane features a white dot in order to count rotations easily. When exposed to sunlight or artificial light, the vanes turn with no apparent motive power. This effect is due to differential heating of the black and silver vanes.