The brighter — the warmer? Life experience tells us that these two concepts are inseparable. however, the laws of chemistry refute this interdependence: matter can glow “cold,” with no heating at all. And what is most surprising — such phenomena occur literally everywhere. To illuminate a room, you can switch on a light bulb, but if you are in a dark grove, you will have to build a fire. The bigger the fire, the more light there is. You can also warm yourself up if the night is cold. In the morning, a natural light source will be back — the sun, heated up to 6000 K, giving Fluorite crystals can glow when heated — the process of thermoluminescence. Fluorite is a typical fluorescent mineral, but when it is warmed up or irradiated with ultraviolet light, it starts to phosphoresce. For matter to fl uoresce, an electron in its atom must reduce its energy, that is, move to a lower energy level, emitting the excess energy as a particle of light, a photon. But first, the electron absorbs energy and gets into an excited state. It stays there for a while and, at an arbitrary moment, jumps down, emitting a photon. There are many electrons, so photons are emitted almost at all times, and the substance glows continuously and gradually dies away while the number of excited electrons decreases.