The radiometer is an instructive object which demonstrates the scientific theory of converting natural light into energy. Powered only by light itself, it will spin slowly in low light conditions, furiously in direct sunlight or well-lit rooms up to 2,000 revolutions per minute. It remains unresponsive to LED or fluorescent light. Science lesson aside, this blown glass radiometer functions as an engaging and sculptural object in its own right, perfect for a windowsill, bookshelf, or desktop. Made in Germany.