Date Time New advancement in Nanophotonics explains how collections of hot nanoparticles cool down Everyone has sat outside on a sunny day and been warmed by the sun’s rays. This happens through a process known as radiative heat transfer: the sun emits light (electromagnetic radiation), which travels to the Earth and heats up the objects that absorb it. Radiative heat transfer is also the mechanism behind thermal cameras. Every hot object, including human beings, emits light, allowing it to release heat and thermalize to the environment. The wavelengths, or colors of light that are emitted, depend on the temperature of the object, with the sun being hot enough to produce visible light and human bodies emitting light that is not visible to the eye but can be picked up by infrared sensors.