At first sight, the radiometer looks like an upright standing light bulb, but it is not its purpose to glow. In the sun- or even in normal daylight the wheel inside the bulb starts to turn around. The brighter the light the faster the wheel turns.
The four leaves of the wheel are small plates, which are black on one side and white on the other. The explanation for the constant turning is that the black sides heat up much faster than the white sides, which then also results in heating the air next to the black sides much stronger than the air next to the white sides. Particles in hot gases (and air is nothing more than a gas) move much faster than in cold gases and this results in much more and stronger hits of the black sides, which then results in a constant turning.
The Radiometer is made out of glass with a plastic base.