Luminous Sources

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Light Production

Luminous source• Produces its own light• Example: sun, light bulb, lit

match

Non-luminous source• Does not produce own light• Seen only by using

reflected light

Luminous Sources

• Incandescence• Electric discharge• Phosphorescence• Fluorescence• Chemiluminescence• Bioluminescence• Triboluminescence• Light-emitting diode (LED)• Laser

Heated tungsten filament glows

Incandescence • Production of light as a

result of high temperature• Air from bulb removed and

replaced with non-reactive gas

• Prevents filament from reacting with oxygen and bursting into flame

• 5-10% of energy converted to visible light

• Most converted to infrared light (heat)

• Inefficient

Electric Dischargelight production by passing an electric current through a gas

Electric Discharge

• Neon lights = Geissler tubes (1855)• Vacuum pump removed most of the air from a closed tube• Remaining air glowed when an electric current passed through• Colour of glow depended on gas inside tube

Phosphorescence• Light production by the absorption of UV light

resulting in the emission of visible light over an extended period of time

• Objects coated with phosphors that absorb UV light. Phosphors keep some of the energy and over time release some of the lower energy as visible light.

• Example: glow-in-the-dark

Fluorescence

• Light production by the absorption of UV light resulting in immediate emission of visible light

• Example: fluorescent dyes in detergent, highlighter pens, fluorescent lighting

Fluorescent Light

Structure of Fluorescent Lights• Light tube filled with low-pressure mercury vapour and an inert gas

(e.g. Argon)• Inner surface of tube coated with fluorescent material known as

phosphors

How Fluorescent lights work (video) 1. Electric Discharge: Electric current causes Hg atoms to emit UV light2. Fluorescence: UV light strikes phosphors which convert the energy

into visible light

Fluorescent Light

Pro• Same light output as

incandescent bulb but less heat produced

• Uses less electricity for same amount of light

• Lasts longer

Con• More expensive than

incandescent bulbs• Contain mercury and

should be treated like hazardous waste for disposal

Chemiluminescence

• Production of light as the result of a chemical reaction

• “Cold light”: Little to no heat is produced

Chemiluminescence

How light sticks work:• One chemical in a

narrow small glass vial• Other chemical in main

body• Bending stick breaks

glass vial• Chemical mix in the

main body• Reaction produces

visible light

• Camping• Law enforcement• Military personnel• Entertainment venues• Emergencies• Underwater divers (source

has no moving parts, completely sealed)

• Hazardous environments where a spark could be dangerous (source does not require electric current)

Chemiluminescence Application

Bioluminescence• Production of light in living organisms as a result

of a chemical reaction• Little to no heat produced• Function: protection from predators, lure prey,

attract mates• Example: luciferase enzyme in fireflies catalyze

oxidation of luciferin protein to produce light

Angler Fish

Bioluminescence• Green Fluorescent Protein (GFP): exhibits bright

green fluorescence when exposed to blue light• Originally discovered in jelly fish• Now used extensively in research as a marker

for gene expression

Triboluminescence• Production of light from friction (rubbing), pressure

(crushing) or mechanical shock (scratching) • Explained by the breaking of chemical bonds in the

material• Most often seen in rubbing of certain crystals• Also works with Wintergreen hard candy, pulling apart 2

pieces of duct tape, peeling transparent Scotch tape

Light-emitting diode (LED)

• Production of light by an electric current flowing in a diode

• Diode: a simple type of semiconductors

• Semiconductor: a material that allows electric current to flow in only one direction

• Applications: Christmas lights, traffic lights

Light-Emitting Diode Comparison

Compared to incandescent bulbs

Pros• No filament (doesn’t burn out)• Not much heat production (less

wasted energy)• More energy efficient (longer

lifespan, lower power usage)

Cons• Produces a cool ‘blue’ light

instead of the warm ‘yellow’ light

Compared to compact fluorescent bulbs

Pros• No toxic mercury• More energy efficient (longer

lifespan, lower power usage)

Cons• Higher up-front costs

LASER

• Light

• Amplication by

• Stimulated

• Emission of

• Radiation

Properties of Laser LightLasers • emit wavelengths of

the same energy level• results in a light beam

of a single pure colour• monochromatic

Incandescent• emit wavelengths of

many different energy levels

• results in white light (combination of all colours)

Properties of Laser Light

• Waves are directional (travel in the same direction)

• Results in light that is concentrated into one narrow beam and can travel great distances without spreading out

• Waves are coherent (wave fronts launch in unison)

• Results in light that is very intense

Application of Lasers- Manufacturing: cutting glass, burning through steel

- Astronomy: measure Earth-moon distance

- Research: surveyor to measure distance

- Entertainment: laser light shows

- Military: Boeing airborne laser, tactical high energy laser

- Media technology: CD, DVD

Military Application of LasersAirborne Laser (ABL) (video)

Military Application of Lasers

Tactical High Energy Laser (THEL) (video)

Media Technology Application• CD & DVDs are read by lasers• Pits: bumps on discs that scatter laser light

in all directions• Land: non-bumps that reflect laser light• Reflected light is converted into binary

code (0’s and 1’s)

DVD & Blu-Ray Construction

DVD Blu-Ray

Laser Red Blue

Wavelength 650 nm 405 nm

Pit 0.4 µm 0.15 µm

Track pitch 0.74 µm 0.32 µm

Storage 4.7 GB 25 GBhttp://electronics.howstuffworks.com/blu-ray1.htm

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