About Solar Radiometers

Solar radiometers are also known as light mills because light moves their blades as opposed to wind for windmills. They consist of an airtight bulb containing a partial vacuum. Inside the glass bulb is a fine vertical spindle with a set of vanes mounted at the top. When the glass bulb is exposed to light, the vanes are propelled around, the speed of propulsion increases with the intensity of light, providing a qualitative way of measuring electromagnetic radiation.

The Crookes radiometer was invented by the chemist Sir William Crookes as the by-product of some chemical research. In the course of very accurate quantitative chemical work, he was weighing samples in a partially evacuated chamber to reduce the effect of air currents, and noticed the weightings were disturbed when sunlight shone on the balance. Investigating this effect, he devised the device named after him, still manufactured and sold to this day as a curiosity item.

This version is both a scientific curiosity and a beautiful ornament. These days the Solar radiometer, or Crookes radiometer, is more of a beautiful science gizmo than a means of accurate measurement. Our Solar Radiometer shop stocks a range of exquisite radiometers which make unusual and interesting gifts for scientists and science enthusiasts.