Glow of common light sources (such as lights, flame, Sun Shine) is a substance in the external energy (such as solar energy, electric energy, heat, and so on) when atom in the electrons can absorb energy from outside a lower jump to the high energy level, that is, atoms are excited. Inspire is a "stimulated absorption" process. In the high energy level of e-life is very short (typically 8-10 seconds), without outside spontaneously under the effect of low energy level transitions, transitions will produce light (electromagnetic) radiation.
This radiation is known as spontaneous emission. Atomic spontaneous emission process is a stochastic process, each glowing Atomic luminescence processes separate, unrelated, namely light radiation by emission direction is random shooting in all directions, no phase, not the same polarization. Because the excitation level has a width, so the frequency of the emitted light is not a single, and has a range of.
Under normal conditions of thermal equilibrium, in the high energy level of the atom number density is much lower than the density of atoms at a low level, this is because at the level of atoms when the density index decreases with the increase in energy levels e, this is the famous Bohr Boltzmann distribution law. Visible at 20 ℃, almost all hydrogen atoms in the ground state, to make the Atomic glow, you must provide energy that atoms get excited, so the common broad glow contains stimulated absorption and spontaneous emission processes. In General, the energy of radiation light source is not strong, and launched in all directions, more away energy.