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Producing Visible Light

Section 10.2

Pgs. 394-398

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Producing Visible Light

  • The most important natural source of light on Earth is the Sun.
  • Other natural sources of light include light from stars, fire, and lightning.

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Sources of Light

  • Light produced by the Sun or other stars is called natural light.
  • Light produced through human technology is called artificial light.

Hmm… Does the moon produce natural light? What do you think?

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Incandescent Light

  • Incandescent light is produced by an object that is at a very high temperature.
  • Electric current flows through the metal filament causing it to glow and emit light.
  • Very inefficient. Only 5% of the electric energy is converted into light. Most of the energy is released as heat.

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Fluorescent Light

  • Fluorescent light is emitted by some substances when they are exposed to electromagnetic radiation.
  • The bulb is filled with mercury vapour and coated with phosphor (white powder that glows when exposed to energized particles).
  • Electric current passes through the bulb causing the gas inside to glow.
  • More efficient, but still releases 80% of their energy as heat.

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Chemiluminescence

  • Chemiluminescence is light produced from a chemical reaction without a rise in temperature.
  • This is referred to as `cool light` because it gives off very little heat.
  • All forms of bioluminescence are special kinds of chemiluminescence.

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  • The ability of a plant or animal to produce light is called bioluminescence.
  • Some algae, jellyfish, insects, crustaceans, bacteria, earthworms, and fungi produce light.

Bioluminescence

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Phosphorescent Light (glow-in-the-dark)

  • Phosphorescence is the ability to store energy from a light source and then emit it slowly over a long period.
  • The light eventually fades, but can be re-energized if held close to a light source.

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Triboluminescence

  • Triboluminescence is the production of light from friction.
  • Some crystals cam be made to glow by rubbing them together or crushing them.

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Electric Discharge

  • Electric discharge is a method of producing light in which an electric current passes through the air or another gas (neon).
  • Lightning is an example of electric discharge through the air.
  • Neon lights produce light by discharging electricity through the element neon causing to glow intensely.

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Light-Emitting Diode (LED)

  • Electroluminescence is the process of transforming electrical energy directly into light energy.
  • A light-emitting diode (LED) is an electroluminescent light source made out of a material called a semiconductor.
  • A semiconductor is a material that can be made to change how well it conducts electricity.

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  • Some semiconductors can be made to emit light when a small electric current is passed through them.
  • Light-emitting diodes provide the backlight for many handheld devices.
  • Even more energy efficient than fluorescent light and take far less time to light up.

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Plasma Displays

  • In a plasma display, each colour is a tiny fluorescent light in which an electrical signal causes a gas (such as neon) to illuminate as red, green, and blue light.
  • By varying the brightness of each primary colour, millions of colours can be produced.

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Organic Light-Emitting Display (OLED)

  • An organic light-emitting display (OLED) is a light source made of several extremely thin layers of organic molecules that use an electric current to produce light.
  • OLEDs use less energy that other displays because they do not require a backlight, they are thinner, lighter, brighter, and more flexible.
  • OLED technology is new and has potential applications to screens of electronic devices, TV screens and computer screens.

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Liquid Crystal Displays (LCD)

  • In liquid crystal display (LCD), a white light shines behind a liquid crystal.
  • A liquid crystal is a solid that can change the orientation of its molecules (like a liquid), but only when electricity is applied.
  • Electric current causes the liquid crystal to alter their positioning which emits light.
  • Special filters, called polarizing filters, are placed in front of the crystals to produce any colour of light.

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Seatwork / Homework

  • Read Section 10.2 (p. 392 – 398)
  • Learning Checkpoint # 1 – 5 (p. 395)
  • Learning Checkpoint # 1 – 5 (p. 398)
  • Check and Reflect # 1 – 12, 15 (p. 401)