Atoms are perpetual motion. They constantly vibrate, move and rotate. Even the atoms that make up our seats are constantly moving. There are several different excitation states of the atom. In other words, they have different energy. If we give a large amount of energy to an atom, it will get rid of the ground state level and reach the level of excitation. The level of excitation depends on how much energy is applied to atoms in the form of heat, light or electricity.
Atoms consist of nuclear (including protons and neutrons) and electron clouds. We can imagine the electrons in the electronic cloud moving around the nucleus in different orbits. It is not yet possible to observe the discrete orbit of electrons, but it is easier to think of these orbitals as different levels of atoms. In other words, if we apply a certain amount of heat to the atom, it is foreseeable that some electrons in the low energy orbit will be transferred to the high energy orbit, that is, farther away from the nucleus.
After electron transfer to high energy orbit, the electron will eventually return to the ground state. In this process, electrons will release energy in the form of photons (a light particle). You will find that atoms are constantly releasing energy in the form of photons. For example, when the heater in the toaster oven turns bright red, it is because the atoms are excited by heat and red photons are released. The electrons in the excited state have higher energy than the unexcited electrons, and it is precisely because the electrons have absorbed a number of energy to reach the level of excitation, which releases the energy to the ground state. This energy will be released in the form of photons (light energy). The emitted photon has a specific wavelength (color), depending on the energy of the electron when the photon is released.
Night vision sight
Any living creature consumes energy, and so does many inanimate objects, such as engines and rockets. Energy consumption produces heat. In turn, heat causes the atoms in the body to emit photons in the thermal infrared spectrum. The higher the temperature of a body, the shorter the wavelength of the infrared photon will be released. If the temperature of an object is very high, the photons it sends can even enter the visible light spectrum, starting with red light, then orange, yellow, white, until blue light.