Sources of Light

Question 1

Incandescence

Answer 1

• heat a tungsten filament to very high temperature using electrical energy
• the filament releases some of its energy as light
• 5% efficient
• example = incandescent light bulbs

Question 2

Fluorescence

Answer 2

• fluorescent tubes are coated with a phosphor (on the inside) and contain mercury vapour
• electrical current flowing through the tube excites the mercury atoms
• the mercury atoms give off the energy as invisible ultraviolet light
• the UV striking the phosphor causes it to glow
• 20% efficient
• example = compact fluorescent bulbs

Question 3

Phosphorescence

Answer 3

• a variation of fluorescence in which the phosphor absorbs UV light, but doesn’t return all the energy right away
• phosphorescent objects glow for many hours after being exposed to a bright light
• example = glow in the dark toys

Question 4

Electrical Discharge

Answer 4

• electrical current flows through a gas, exciting the atoms
• the atoms glow with a characteristic colour
• example = lightning

Question 5

Light Emitting Diode

Answer 5

• electroluminescent devices that convert electrical energy directly to light
• a semi conductor emits light when electricity passes through, without generating heat
• example = electric billboard

Question 6

LASER

Answer 6

• light amplification by the stimulated emission of radiation
• unlike normal light, they produce highly focused, intense, narrow beams
• example = bar-code scanners

Question 7

Chemiluminescence

Answer 7

• atoms’ electrons are excited due to a chemical reaction, rather than by being exposed to electricity or UV
• the excited electrons release their excitation energy as wavelengths of visible light
• example = glow sticks

Question 8

Bioluminescence

Answer 8

• a form of chemiluminescence in living organisms
• common in abyssal creatures that live deeper in the ocean than light can penetrate
• example = fireflies

Question 9

Triboluminescence

Answer 9

• production of light by crushing or breaking crystals

* example = breaking sugar crystals

Question 10

Organic Light Emitting Diode

Answer 10

• light source made of extremely thin layers of organic molecules uses different organic molecules to emit different colours
• example = cell phones

Question 11

Plasma Displays

Answer 11

• each colour is a tiny fluorescent light with an electrical signal which causes a gas to release UV radiation
• then phosphorus absorbs the light
• example = plasma screen

Question 12

Liquid Crystal Displays

Answer 12

• a white light shines behind a liquid crystal
• the crystal blocks or transmits light depending on the amount of electricity
• example = computers