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Light is a form of radiant energy (energy that travels through space in waves).

The Spectrum

Light that we see, called "visible light", is only part of the electromagnetic spectrum:

  • Cosmic Rays
  • Gamma Rays
  • X-Rays
  • Ultraviolet Light
  • Visible Light
  • Infrared Light
  • Microwaves
  • Radio Waves

Sometimes we call visible light: "White Light".  It contains the colors of the rainbow (spectrum):

   Red   Orange   Yellow   Green   Blue   Indigo   Violet         (Roy G. Biv)

If you shine white light through a prism, it is separated into these colors.


There are three primary colors of light:

  • Red
  • Blue
  • Green

In our eyes, we have cones (color-sensing cells) that "see" red, blue and green.  (This is why these are the primary colors of light.)


Just like with paints, mixing primary colors gives you secondary colors:

  • Red + Green = Yellow
  • Green + Blue = Cyan
  • Blue + Red = Magenta

If you combine all three of the primary colors, you get... White Light!


The Eye 

We detect light with our eyes.  There are 12 parts to the eye that we covered in class...

  1. Sclera - The tough outer covering that makes up the white part of your eye.  The sclera protects the eye.
  2. Cornea - The clear part of the sclera that is in front of the iris and pupil.  This lets light into the eye.
  3. Choroid - The layer just below the sclera, it contains blood vessels to nourish the eye and brings nerves into the eye.
  4. Iris - The colored ring in your eye.  The iris opens and closes to control the amount of light that passes through the pupil.
  5. Pupil - The "black dot" in the center of your eye - it's really a hole in the iris that allows light to enter the eye.
  6. Lens - Just behind the iris and pupil, the lens focuses the light onto the retina in the back of the eye.
  7. Ligaments - Tiny fibers that connect the lens to the ciliary bodies.
  8. Ciliary Bodies - Tiny muscles that pull on the ligaments to change the shape of the lens.  When they pull, the lens gets thinner.  When they relax, the lens gets thicker.  This changes the focus of the lens.
  9. Aqueous Humor - Fluid in the front compartment of the eye (between the lens and the cornea) that helps they eye keep its shape.
  10. Vitreous Humor - Fluid in the rear compartment of the eye (behind the lens) that helps they eye keep its shape.
  11. Retina - The inner lining of the eye.  The retina contains rods and cones, which convert light into nerve impulses.
    • Rods - Sensory cells that see in black and white, but allow you to see shapes.
    • Cones - Sensory cells that allow you to see color.  Humans have 3 types of cones: red, blue, and green.  Birds and turtles have a fourth type that lets them see in ultraviolet.
  12. Optic Nerve - Brings the nerve impulses (signals) to the brain.

Behavior of Light

Reflection - when light is bounced off of an object without being absorbed.

Absorption - when light is taken in without being reflected or transmitted.

Transmission - when light passes through an object.

Scattering - when light is reflected in random directions.


Angle of Incidence = Angle of Reflection

Incident beam - the beam of light that strikes an object.

Reflected beam - the beam of light that has bounced off of an object.


Refraction - the bending of a light beam (or other wave) as it passes from one medium into another.

Diffraction - the bending of waves as they pass the edges of objects.


Image - the visual impression of an object.  Images can be produced by reflection in a mirror or refraction in a lens.

Real images are formed whem light rays come together, and can be projected onto a screen.  (Images from the projector.)

Virtual images are not formed by light rays coming together, and cannot be projected onto a screen.  (Images in a mirror.)


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