1. Emission of Light from Gases
Gas discharge lamps are demonstrated

2. Purpose
To produce light from a gas and electricity

3. Demonstration
An electric power source was attached to the ends of a glass tube filled with a gas.
The current was turned on and electricity ran through the tube exciting the gas.
Light was emitted.
Gas discharge tube

4. Three Concepts of Emission
Atomic Emission
Spectrum of Light
Energy States

5. Atomic Emission
When an electric current is passed through a gas, the gas emits light.
This is due to the change of energy of the gas. The electrons in the atoms of the gas become excited to a higher energy state (the “excited state”) and when they return to the original, low-energy state (“the ground state”), the atoms of the gas emit the excess energy as light.

6. Spectra
Spectra (plural of spectrum) are composed of different energies which continuously change from high to low. A rainbow is a spectrum of different color and light energies.
The color of the light is determined by the energy of the emitted light, and the energy is related to the wavelength
Different colors are due to different wavelengths of light
Different colors therefore are of different energy

7. Color Spectrum High Energy Low Energy

8. Energy States of Atoms
Ground state - the lowest energy state of an atom or molecule (most stable state) with regard to the position of the electrons around the nucleus
Excited state – results when ground state electrons are excited by energy to higher energy states. Excited states are unstable and an atom in the excited state immediately returns to the ground state.

9. Conclusion
A power supply attached to a gas discharge tube will send an electric current from one electrode, through the gas, to the other electrode.
This excites the gas atoms to their excited state, and in turn they return to the ground state and emit a color of light depending on the energy released.

10. Comments
Neon signs that you see all over town work upon the concept of gas discharge lamps. The different colors of the signs are from either using different gases or colored tubes.
Fluorescent lights are similar but are coated inside with a chemical that emits light in the presence of electrical energy

11. Quiz
Would changing the gas inside the tube affect the color of light emitted?
When the current of electricity runs through the tube do the atoms have a higher energy or lower?
Is the wavelength proportional to the energy released?
When does the atom release the energy as light - in the ground state or in the higher energy state?
What is a common use for gas discharge lamps?