Optics - Physics

• Incandescence


  Light emitted because an object is very hot
• Luminescence


  Light that is emitted in the absence of heat
• Sources of light


  • Light from the Sun
  • Light from Incandescent Light Bulbs
  • Light from Electrical Discharge
  • Fluorescence
  • Phosphorescence
  • Chemiluminescence
  • Bioluminescence
  • Triboluminescence

  
• Light from the Sun

  • Most abundant source of light
  • Hydrogen atoms in the Sun's core have so much energy that they collide and form helium - fusion reaction
  • Fusion reactions release a lot of energy
  • This fusion energy is transmitted to the outer layers of the sun and will excite the atoms, which leads to the release of excess energy in the form of light
• Light from Incandescent Light Bulbs

  • These light bulbs have a tiny tungsten wire that starts to heat up and glow when electric current is run through
  • The electrical energy run through excites the atoms
  • Inefficient at producing light - only 5% of energy used becomes light (other 95% lost as heat)

  
• Light from Electrical Discharge

  • Emitted light is from electric current passing through vapour and exciting the atoms
  • When excited atoms release their energy they emit light (commonly yellow)
  • Examples: lightning and sodium vapour lights (streetlights)
  • Drop of sodium and mercury placed into bulb and air removed, leads to mercury and sodium forming vapours, electricity run through and excites these vapour atoms which emit light

  
• Types of Luminescence


  • Fluorescence
  • Phosphorescence
  • Chemiluminescence
  • Bioluminescence
  • Triboluminescence
• Fluorescence


  • Light emitted during exposure of the source to ultraviolet light
  • Fluorescent light bulbs common example
  • Electrical energy passed through electrons and emit electrons, electrons travel through gas in the bulb and excite mercury atoms in the gas
  • Excited mercury atoms release excess energy in the form of UV light
  • Light bulbs coated in powder called phosphor that absorbs the UV light and emits it as visible light
  • Fluorescent light bulbs 20% efficient (compared to 5% of incandescence)

  
• Uses of Fluorescence


  • Crime scenes: many bodily fluids, such as blood and urine contain fluorescent molecules. Forensic scientists can shine UV light in crime scenes to check for these fluids
  • Tongue Health: Dentists can shine blue light on the tongue as abnormal tissue can be fluorescent
  • Documentation: can make documents from fluorescent materials to check for legal documents
  • Theatre: Some theatre performers use paint with fluorescent dyes. When the theatre is dark and only ultraviolet light is shining on the performers, all the audience can see is the fluorescent light coming from the paint
• Phosphorescence


  • Similar to fluorescence except excited atoms retain energy for longer after they have absorbed UV light
  • Glow in the dark objects use this

  
• Chemiluminescence


  • Light generated as a result of a chemical reaction
  • Glow sticks

  
• Bioluminescence


  • Light produced by living organisms
  • Chemical reactions in living cells will produce light
  • Fireflies and many marine organisms use this

  
• Importance of Bioluminescence
• Triboluminescence


  • Light produced by mechanical, physical means
  • Smashing two rocks together
  • Crushing of white light savers
• The refractive index is the ratio of the speed of light in vacuum to its speed in that medium.
• A prism separates white light into different colours because it has a different refractive index for each colour, causing them to bend at slightly different angles.
• When light travels from one transparent material to another with a higher refractive index, it bends towards the normal (refraction).