PRODUCTION OF LIGHT

Production of LightObjects 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

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

2. Light from Electric DischargeElectric Discharge – the process of producing light by passing an electric current through a gas. Ex #1: LightningElectricity passing through air (mixture of gases)

Ex #2: Neon signsElectricity passing through different gases & producing different colours.

3. Light from PhosphorescencePhosphorescence– 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

4. Light from FluorescenceFluorescence – 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.

4. Light from FluorescenceEx #2: Fluorescent lightElectric current applied mercury atoms emit UV light UV light strikes fluorescent coating Visible light given off

5. Light from ChemiluminescenceWhat does the name suggests?Chemiluminescence is the production of light as a result of chemical reaction, with little or no heat produced.

Example: Glow stickBreaking the glass chamber in the stick mixing of chemicals in the stick light produced

6. Light from BioluminescenceThe 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.

Bioluminescence

7. Light from TriboluminescenceThe production of light when certain crystals are scratched, crushed or rubbed.

Example: striking 2 sugar cubes against each other.

8. Light from a LEDLED (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

11.3 - LASERLASER: Light Amplification by Stimulated Emission of RadiationProduces electromagnetic waves of the same Energy level so no separation of colour when going through triangular prism. Very pure colour emitted.

LASERVery intense (as waves travel in same direction and are in unison)

LASERLaser’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)