LED Cooling Power for Ice Production · Physics Brawl 2025 #7
Physics · thermodynamics
Problem
David read a study stating that LEDs in a laboratory have an electrical input power of Pele=30 pW, but an optical output power of Popt=69 pW, which would correspond to an efficiency greater than 100%. At first, he was surprised, but then realized that part of the power comes from thermal energy. How many diodes would be needed to produce an ice cube with a volume of V=10 cm³ in one hour, assuming we have water at a temperature of 20°C? Assume that all optical power comes from the heat of the water and the electrical source. The optical power is independent of temperature, and heat transfer from the surroundings is negligible.