Please add detail, and answer where the light comes from. thank you!
air absorbs uv ray. air gets hot and emits light
neon is not mandatory there, it only give specific color. any gas under low pressure allow glow discharge. electrons, that accelerated by electric field, under light vacuum have a chance to get big kinetic energy before next collision. and collision with atom with big speed will cause radiation
For neon lights, and lights using the other noble gases, an electric charge is used to excite an electron in the gas up to an excited state. When it falls back to the ground state, it emits energy in the form of light. The mercury vapor in a fluorescent light does the same thing, but the light it emits is ultraviolet light, which we can't see. That light is in turn absorbed by a layer of fluorescent material on the inside of the tube, which emits visible light when struck by ultraviolet light.
