Ch 18

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Ch 18

• Light and Color

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Electromagnetic radiation

• Transverse waves
• Do not need a medium

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Radio Waves

• a) low frequency
• b) long wavelength
• c) low photon energy

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Infrared (IR)

• sunlight
• Heat
• Body gives off IR

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Visible Light

• only part of the spectrum you can see
• ROYGBIV

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Ultraviolet Radiation

• overexposure can damage skin cells
• ozone layer protects us from most UV

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X-Rays

• can travel through skin and muscle
• absorbed by denser materials such as bone
• used for taking pictures of bones

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Gamma Rays

• highest frequency, shortest ?
• can be used to kill cancerous cells

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LIGHT AND COLOR

• What you see depends on
• 1) the amount of light the objects you are
  looking at are reflecting or absorbing
• 2) color of light the objects you are looking at
  are reflecting or absorbing

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LIGHT AND COLOR

• In order for you to see an object, it must
  reflect at least a little bit of light

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Light Transmission

• Opaque Materials-absorb or reflect all light and
  you cannot see objects through them

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Light Transmission

• Transparent Materials-allow light to pass through
  and you can clearly see objects through them

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Light Transmission

• Translucent Materials-allow light to pass through
  but you cannot clearly see objects through them

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Wave Properties of Light

• REFLECTION
• occurs when a wave strikes an object and bounces
  off-occurs with all types of waves
• REFRACTION violet bends most
• the bending of waves caused by a change in their
  speed-amount of bending depends on the speed of
  light in both materials -slows down when
  going through matter

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Wave properties of light

• DIFRACTION
• -the bending of waves around a barrier
• POLARIZATION
• -light vibrates in one plane, horizontal or
  vertical

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Polarization

• Polarization
• Light with waves that vibrate in one plane is
  polarized light
• Horizontal filter blocks waves vibrating on a
  vertical plane
• Vertical filter blocks waves vibrating on a
  horizontal plane

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Polarization
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COLOR

• white objects appear white b/c they reflect all
  colors of light
• black objects appear black b/c they absorb all
  colors of light
• A filter is a transparent material that transmits
  one or more colors of light, but absorb all others

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COLOR

• Primary colors of light are red, green, and blue
• Combine to produce white light so they are called
  additive colors

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PIGMENTS

• a colored material that absorbs some colors and
  reflects others
• 3 primary pigment colors are yellow, magenta and
  cyan
• the 3 pigments combine to produce black so they
  are called subtractive colors

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Colors

• rods allow you to see dim light
• cones allow you to see colors

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Invisibility Cloak

• The Cloak
• The cloak that enables optical camouflage to work
  is made from a special material known as
  retro-reflective material.

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• To understand why this is unique, look at how
  light reflects off of other types of surfaces. A
  rough surface creates a diffused reflection
  because the incident (incoming) light rays get
  scattered in many different directions. A
  perfectly smooth surface, like that of a mirror,
  creates what is known as a specular reflection --
  a reflection in which incident light rays and
  reflected light rays form the exact same angle
  with the mirror surface. In retro-reflection, the
  glass beads act like prisms, bending the light
  rays by a process known as refraction. This
  causes the reflected light rays to travel back
  along the same path as the incident light rays.

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• The result An observer situated at the light
  source receives more of the reflected light and
  therefore sees a brighter reflection.
  Retro-reflective materials are actually quite
  common. Traffic signs, road markers and bicycle
  reflectors all take advantage of retro-reflection
  to be more visible to people driving at night.
  Movie screens used in most modern commercial
  theaters also take advantage of this material
  because it allows for high brilliance under dark
  conditions. In optical camouflage, the use of
  retro-reflective material is critical because it
  can be seen from far away and outside in bright
  sunlight -- two requirements for the illusion of
  invisibility.

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• The retro-reflective garment doesn't actually
  make a person invisible -- in fact, it's
  perfectly opaque. What the garment does is create
  an illusion of invisibility by acting like a
  movie screen onto which an image from the
  background is projected. Capturing the background
  image requires a video camera, which sits behind
  the person wearing the cloak. The video from the
  camera must be in a digital format so it can be
  sent to a computer for processing.
• ComputerAll augmented-reality systems rely on
  powerful computers to synthesize graphics and
  then superimpose them on a real-world image. For
  optical camouflage to work, the hardware/software
  combo must take the captured image from the video
  camera, calculate the appropriate perspective to
  simulate reality and transform the captured image
  into the image that will be projected onto the
  retro-reflective material.

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