Light production
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Light production






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  • Sometimes there is mercury vapour inside the glass tube (how fluorescent bulbs are made – national geographic) (how fluorescence in bulbs works, links ideas of fluorescence and electric discharge with neon tubes)
  • Sometimes there is mercury vapour inside the glass tube
  • http://www. youtube .com/watch?v=0LKk1bTL6fk (ABL) http://www. youtube .com/watch?v= qpuU - BEadxI (THEL)
  • http://www. youtube .com/watch?v= qpuU - BEadxI
  • Answer pg 469 Q #1, 5, 9, 10

Light production Light production Presentation Transcript

  • Luminous Sources
  • 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
  • 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
    Heated tungsten filament glows
  • Electric Discharge
    • light 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)
    • Electric Discharge: Electric current causes Hg atoms to emit UV light
    • 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
    • L ight
    • A mplication by
    • S timulated
    • E mission of
    • R adiation
  • Properties of Laser Light
    • Lasers
    • 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 Lasers
    • Airborne 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 25 GB 4.7 GB Storage 0.32 µm 0.74 µm Track pitch 0.15 µm 0.4 µm Pit 405 nm 650 nm Wavelength Blue Red Laser Blu-Ray DVD