A radiometer is a scientific instrument designed to measure the intensity of electromagnetic radiation, particularly in the form of light. It typically consists of a set of vanes mounted on a spindle, which rotate when exposed to light. The rotation occurs due to the differential heating of the vanes, allowing researchers to quantify the energy of the incoming radiation. Radiometers are used in various fields, including meteorology, astronomy, and environmental science. They help scientists understand energy transfer processes, study the sun's radiation, and monitor climate change by measuring the Earth's energy balance.