light production
TRANSCRIPT
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Luminous Sources
http://afonson311.files.wordpress.com/2011/03/sunset.jpg
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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
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Luminous Sources
• Incandescence• Electric discharge• Phosphorescence• Fluorescence• Chemiluminescence• Bioluminescence• Triboluminescence• Light-emitting diode (LED)• Laser
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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
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Electric Dischargelight production by passing an electric current through a gas
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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
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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
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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
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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) http://www.youtube.com/watch?v=ur5yPa4_j3c&NR=1 1. Electric Discharge: Electric current causes Hg atoms to emit UV light2. Fluorescence: UV light strikes phosphors which convert the energy
into visible light
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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
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Chemiluminescence
• Production of light as the result of a chemical reaction
• “Cold light”: Little to no heat is produced
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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
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• 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
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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
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Angler Fish
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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
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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
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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
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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
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LASER
• Light
• Amplication by
• Stimulated
• Emission of
• Radiation
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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)
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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
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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
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Military Application of LasersAirborne Laser (ABL) (video)http://www.youtube.com/watch?v=0LKk1bTL6fk
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Military Application of Lasers
Tactical High Energy Laser (THEL) (video)http://www.youtube.com/watch?v=qpuU-BEadxI
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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)
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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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http://electronics.howstuffworks.com/blu-ray2.htm