Question

Neon Lights and Discharge Lamps

•Why do lighted signs have different colors?

•Provide a basic design for a discharge lamp and explain the function of the different components.

•Explain the basic structure of an atom and relate it to the color of light produced by discharge lamps.

•Explain why discharge lamps emit only certain colors.

•Design a discharge lamp to emit any desired spectrum of colors.

Answer 1

1. Lighted signs have different colors because they use gas discharge tube to emit lights. The element used within these discharge tubes decided the color emitted. Diffferent elements emit different colors. For example, Neon lights use Neon gas which emits an orange light, similarly other gases will emit different light, like hydrogen emits red color and hemium emits yellow, etc.

2. In a discharge lamp, electricity is sent through an ionized gas held in an arc tube, to produce certain colors depending on the atomic structure of the gas.

Discharge lamps contains -

(i) An arc tube where the gas is held.

(ii) An Electrode, as a cathode it acts as an electron emitter and as an anode it acts like a collector of electrons. It is responsible for the energy to leave and enter.

(iii) Voltage power source

(iv) Ballast to control the process.

3. Atoms have certain energy level of electrons, electrons are allowed to move between only these levels and the intermediate energy is nor absorbed neither released by an electron. When an atom absorbs a photon of energy equal to or more than the energy required for an electron to move to a level above, it gets excited. In an excited state, it is relatively unstabe and quickly releases energy to return to it's normal state. The wavellength of the emitted light is unique to the type of atom used and it's energy levels, producing a specific colour during emission.

4. Discharge lamps emit only certain colors because, the colour depends on the type of the atoms used, the pressure and the density of the gas. For a certain atom, a cetain wavelength is emitted, and hence a certain colour is seen.