Introduction to Light

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Introduction to Light
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Review

• We can see our surroundings because light bounces
  off of objects and into our eyes.

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Electromagnetic Spectrum

• The electromagnetic spectrum is made up of
  different sized wavelengths.
• Humans are only able to see the visible
  portion of the electromagnetic spectrum.

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• The shortest wavelengths are gamma waves.
• The longest wavelengths are radio waves.
• All of the different wavelengths combine together
  to form a continuous spectrum.

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SOURCES OF LIGHT
Light is given off by an object because it is
hot is called INCANDESCENCE.   Light given off
by an object without needing to become hot is
called LUMINESCENCE.
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Light from the Sun

• The Sun is the most abundant source of light.
• When energetic hydrogen atoms at the center of
  the sun collide, they sometimes combine or fuse
  to form helium. These reactions are called fusion
  reactions.

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Light from the Sun

• When the gases on the outer layer of the sun
  release some of their excess fusion energy, the
  energy is emitted as sunlight.

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Light from Incandescence Bulbs

• Incandescent light bulb an electrical current
  runs through a thin tungsten wire. The electrical
  energy generates heat, which then excites the
  atoms in the wire. As the excited atoms release
  their energy they emit light.

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Light from Incandescence

• 5 of electrical energy is used to generate
  light, 95 is lost as heat.
• Incandescent light bulbs are inefficient.

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Light from Electric Discharge

• An electric current is passed through a gas, the
  electric energy excites the atoms of the gas and
  as the gas atoms release their energy they emit
  light.

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Light from Electric Discharge

• Most commonly found in streetlights, the
  characteristic yellow light comes from the
  excited atoms of sodium vapour.

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Fluorescence

• Fluorescent bulb a tube with an electrode at
  each end is filled with mercury vapour and the
  inside walls are coated with a powdery substance
  called phosphor.

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Fluorescence

• An electric current excites the mercury vapour,
  which emits ultraviolet light (not visible).
• The phosphor absorbs the UV light and then emits
  energy in the form of visible light.

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White Light

• Most light sources emit white light.
• White light is a combination of all the colours
  of the rainbow.

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White light in a Prism

• When white light passes through a prism it is
  divided into all of the colours of the rainbow.

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Quick Clip

• Bill Nye Light and Colour introduction

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Answers
White light is (K)
An orange (D)
We dont see things (J)
When white light goes into a prism (A)
A green apple (G)
Chemicals on the skin of fruits and vegetables (B)
Where do all the other colours go? (C)
A black cloth is warm because (F)
A white cloth is not warm because (H)
Blue paint (I)
Red clothing (E)
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Colour Addition Primary Colours
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Colour Addition - Light

• The primary colours of LIGHT are red, blue, and
  green.
• The secondary colours of light are yellow,
  magenta, and cyan.
• When red, blue, and green light are overlapped,
  the result is white light.

R G Y
R B G W
B G C
R B M
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Colour Subtraction

• Consider a white light shining on a shirt that
  absorbs only blue light and reflects all other
  colours
• The shirt is absorbing blue and reflecting red
  and green
• From the theory of colour addition we know that
  red green yellow
• The shirt will appear yellow.

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Colour Subtraction

• The same shirt (still absorbing only blue) has a
  cyan light shone on it (Hint C G B )
• The shirt will appear green.

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Introduction to How We See

• The parts of the eye that allows us to detect
  colour and movement are called rods and cones.

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Rods

• Rods are most sensitive to dark changes, shape
  and movement. They are NOT effective at detecting
  colour.

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Cones

• Cones are used for colour vision and are
  wavelength specific

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Cones

• There are three types of cones

Red Cones Green Cones Blue Cones
Detects long wavelengths (i.e. red, orange, yellow) Detects medium wavelengths (i.e. yellow, green, blue) Detects short wavelengths (i.e. blue, indigo, violet)
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Colour Blindness

• What does it mean if someone is colour blind?

A person is colour blind when one or more types
of their cones are partially or completely
deficient.
Protanomaly Dichromasy Protanopia
Referred to as red-weakness. A protanomalous viewer has trouble detecting the saturation of red as well as the brightness of red. A deficiency of red cones No perceptible difference between red, orange, yellow, and green. All of these colours appear to be the same. A deficiency of red cones and green cones. The brightness of red, orange, and yellow are greatly reduced compared to normal. Protanopes often confuse red to be black or grey. A deficiency of red cones
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Protanomaly

• Notice
• The colour normal berries appear brighter than
  colour deficient.
• Purple is made of blue and red. The colour
  deficient viewer is unable to see the red
  component of the purple berries, so the berries
  appear blue

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What do dogs see?

• While humans have three types of cones, dogs only
  have two types of cones. Research shows that
  dogs are missing the long-wavelength cones (the
  cones that detect red, orange and some yellow).

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• Dogs also have fewer cones than humans so their
  vision is less rich and intense as a humans
  vision

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Colour Vision Facts

• The gene that encodes the red cones lies on the X
  chromosome.
• (Females have two X chromosomes while males only
  have one X chromosome. For this reason, women see
  varying shades of red while most men see only
  fire engine red.)

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Colour Vision Facts

• Bees and butterflies have better colour vision
  than humans. Both insects are able to see colours
  that humans cannot see. Their colour vision
  extends into the ultraviolet region.
• The ultraviolet wavelengths (which are invisible
  to humans) reveal patterns on flowers that guide
  bees and butterflies to the centers of
  nutritious flowers.