Heat. Heat. Where there is life, there's also light.If we look at our cities at night, we see light everywhere. But not only in the streets, but also in our pockets with our smartphones, their displays, with our smart watches, with the smart gadgets that we carry all around us, but also in our homes with our LED lights. In all of these applications, materials and molecules are getting excited by electrical energy and when they return to their ground state, they emit this energy in the form of light.Human li ...