light production
TRANSCRIPT
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) 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
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)http://www.youtube.com/watch?v=0LKk1bTL6fk
Military Application of Lasers
Tactical High Energy Laser (THEL) (video)http://www.youtube.com/watch?v=qpuU-BEadxI
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
http://electronics.howstuffworks.com/blu-ray2.htm