1. Production of Light

2. Production of Light Objects can either be:
Luminous (produce their own light) ex: Sun
Non-luminous  can be seen because it is able to reflect light
Q: So what are the sources for luminous objects?
A: 8 different luminous sources

3. 1. Light from Incandescence
Incandescence – light produced due to high temperature. Ex #1: Regular light bulbs (Thomas Edison) Electricity passes through tungsten wire  becomes very hot and emitted light: ~90% released as Infrared light (not visible to naked eye, but we feel the heat) ~10% released as visible light Ex #2: Metal heated up

4. 2. Light from Electric Discharge
Electric Discharge – the process of producing light by passing an electric current through a gas. Ex #1: Lightning Electricity passing through air (mixture of gases) Ex #2: Neon signs Electricity passing through different gases & producing different colours.

5. 3. Light from Phosphorescence
Phosphorescence– the process of producing light by absorption of UV light by special materials (called phosphors) resulting in emission of visible light over a period of time “Glow in the dark” items

6. 4. Light from Fluorescence
Fluorescence – the immediate emission of visible light as a result of absorption of UV light.
Ex #1: Fluorescent dye in detergent
Clothes look brighter due to extra visible light given off.

7. 4. Light from Fluorescence
Ex #2: Fluorescent light Electric current applied  mercury atoms emit UV light  UV light strikes fluorescent coating  Visible light given off

8. 5. Light from Chemiluminescence
What does the name suggests? Chemiluminescence is the production of light as a result of chemical reaction, with little or no heat produced.
Example: Glow stick
Breaking the glass chamber in the stick  mixing of chemicals in the stick  light produced

10. 6. Light from Bioluminescence
The production of light in living organisms as a result of chemical reaction, with little or no heat produced.
Example: Dinoflagellate is a marine plankton that will glow in presence of danger/predator.

11. Bioluminescence

12. 7. Light from Triboluminescence
The production of light when certain crystals are scratched, crushed or rubbed. Example: striking 2 sugar cubes against each other.

13. 8. Light from a LED
LED (Light-Emitting Diode): an electronic device that allows an electrical current to flow in only one direction.
Need special materials called semiconductors.
Differences from incandescent bulb:
No filament required
Not much heat produced
More Energy efficient
Example: Christmas lights

15. LASER
LASER: Light Amplification by Stimulated Emission of Radiation
Produces electromagnetic waves of the same Energy level  so no separation of colour when going through triangular prism. Very pure colour emitted.

16. LASER
Very intense (as waves travel in same direction and are in unison)

17. LASER
Laser’s unique properties makes it useful in measuring large distances, such as the distance from moon to earth. Q: How do they do it?
Apollo 11, 14 and 15 mission left corner-cube reflectors on the moon.
Distance calculated as 385,000 km (with an accuracy of 3 cm)