Objects can either be:  Luminous (produce their own light) ex: Sun 

Non-luminous

 able to reflect light can be seen because it is Q: So what are the sources for luminous objects?

A: 8 different luminous sources

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

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.

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

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.

Ex #2: Fluorescent light Electric current applied  emit UV light  coating  mercury atoms UV light strikes fluorescent Visible light given off

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

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.

The production of light when certain crystals are scratched, crushed or rubbed.

Example: striking 2 sugar cubes against each other.

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

LASER:

L

ight

A

mplification by

S

timulated

E

mission of

R

adiation  Produces electromagnetic waves of the same Energy level  so no separation of colour when going through triangular prism. Very pure colour emitted.

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

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)