Energy bands and gaps can explain the spectral properties of an incandescent lamp and LEDs. The conduction and valence energy bands and the resulting energy gap result from interactions of numerous atoms that are very close together - a situation that occurs in solids. The energy gap of the solid materials (called semiconductors) that make up the LED determine the energies (and thus, colors) of light emitted by the LEDs.
A solid can be a pure material in which all atoms are the same element. As a result, each nucleus of the atom contained in this solid has the same electrical charge. Thus, each atom in this solid has identical properties. The interactions among these atoms create the energy bands and gaps that we have studied. Modern technology can create materials that are very close to being all identical atoms.