Light

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Light
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Light Facts

• Light The range of frequencies of
  electromagnetic waves that stimulate the retina
  of the eye.
  
• 400 nm 700 nm ( 4 x 10-7 to 7 x 10-7 meters)
• 1 meter 109 nanometers
• Light Speed 3.00 x 108 m/s or 186,000 miles
  / sec
  
• Seen as c in equations E mc2

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The Electromagnetic Spectrum
High Energy (dangerous)
Low Energy (no probs)
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Sources of Light
Whats the difference between the moon and sun?
(in terms of light)
Illuminated Body
Luminous Body
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Sources of light

• Luminous Body
• A body that emits light.
• Illuminated Body
• A body that reflects light.
• Luminous Flux ( P in equations )
• Rate at which light is emitted from a source.
• Units Lumens ( lm ) Best Buys
  Digital Projector Line
  
• Luminous Intensity
• Luminous flux that falls on 1m2 of a sphere 1m in
  radius.
  
• Units Candela, Candle Power ( cd ) Cabelas
  Spotlight Line
  
• Luminsous Flux Luminous Intensity / 4p
• Illuminance ( E in equations )
• How much light falls on a flat surface.
  Illumination.
  
• Units lm/m2 or lux

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The luminous flux is a very basic unit of
measurement for light. If a uniform point light
source of 1 cd luminous intensity (about the
intensity of a normal wax candle!) is positioned
at the center of a sphere of 1 m radius, then
every area of 1 m2 on the inside of that sphere
will receive a luminous flux of 1 lm.
1 cd 4p lumens or 12.57 lm
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• Inverse Square Relationship
• As distance away from light source increases,
  illumination on the surface goes down by the
  distance squared. The Luminous Flux from
  light source stays the same.

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Inverse square law for Luminous Intensity
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Illuminating a Flat Surface

• 2 ways to increase illumination on a flat
  surface
  
• Brighter source (ie brighter bulb)
• Move the source closer to the surface
• Mathematically written as

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Example Problem

• What is the illumination on your desktop if it is
  lighted by a 1750 lm lamp (typical 100 W bulb)
  that is 2.50 m above your head?

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Example 2

• WI state law requires 160 lx of the surface of
  each desk. My lights are 250 cm above the desk
  surface. What is the minimum luminous flux the
  lights must deliver?

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• Transparent Completely clear (glass)
• Translucent Semi Clear. Transmits light, but
  not shapes (wax paper)
  
• Opaque No light transmission (brick wall)

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The Speed of Light
Scale model of Earth and Moon with beam of light
travelling to it
Ole Roemer Danish astronomer who first
quantitatively measured the speed of light in
1676. Found that Io would emerge 13 s faster at

position 1. and 13 s slower at
position 3. He assumed that the moons were orbit
ing at regular
intervals, so something had to
account for the lapse. Theorized light had a fini
te speed, and estimated it
to be near 2.2
x 108 m/s. Accepted value today 299,792,458 m/s
Light
Speed 3.00 x 108 m/s
Light Speed through History
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Color
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• Primary Colors Red, Green, Blue (RGB)
• All colors can be made by adding varying
  intensities of red, green, and blue
  
• Secondary Colors Yellow, Magenta, Cyan
• A secondary color is one that can be made by
  adding 2 primary colors.
  
• Complimentary Colors Blue Yellow, Cyan Red,
  Yellow Blue
  
• Two colors that add up to make white light.

Colors by Addition
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• Pigments Dyes Substances that absorb
  (subtract) certain colors and transmits or
  reflects others. (Example Red absorbs blue and
  green light)
• Primary Pigments Yellow, Cyan, and Magenta
• Pigment that only absorbs primary color. Yellow
  absorbs blue, but reflects red and green.
  
• Secondary Pigments Red, Blue, and Green
• Pigments that absorb 2 primary colors. Red
  absorbs both green and blue.
  
• Note if Yellow dye (absorbing blue light) is
  mixed with Blue dye (absorbing green and red
  light) all light is absorbed and nothing is
  reflected. Hence Black is the result.

Colors by Subtraction
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Dyes in the dice selectively absorb and reflect
various wavelengths of light. The dice are
illuminated by a) white light b) red light c)
blue light.
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Polarization
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