How Do Solar Radiometers Work?

The solar energy is changed first to thermal energy, and then to kinetic energy. A partial vacuum inside the radiometer glass allows the vanes to spin easily. The brighter the light, the more heat energy is transferred, and faster the vanes will rotate.

What do radiometers do?

Radiometer, instrument for detecting or measuring radiant energy. The term is applied in particular to devices used to measure infrared radiation. Radiometers are of various types that differ in their method of measurement or detection.

Why does the radiation not get stopped by the glass of the radiometer?

Movement with black-body radiation

Directly heated glass gives off enough infrared radiation to turn the vanes, but glass blocks much of the far-infrared radiation from a source of warmth not in contact with it.