Bending Light

Make a lens and see how your eye manipulates the light that enters it.


  • Utility or Exacto knife
  • Clear cylindrical drinking glass
  • Water
  • Scotch tape
  • A piece of colored plastic
  • Flashlight
  • Shoebox or similar box, no top needed


  1. Carefully cut 2 vertical slits in one end of the box, you may want an adult to help you. The space between the slits should be smaller than the width of the drinking glass.
  2. Place the colored plastic over one of the slits, and tape it in place.
  3. Turn on your flashlight and darken the room.
  4. Shine the flashlight into the box through the slits.
  5. Look inside the box. What is the light doing? Where do the light rays appear on the side of the box?
  6. Pour water into the glass, and place it in the center of the box. Repeat steps 3 and 4.
  7. What happens to the light beams after they pass through the glass of water?


The box is a model of your eye. Light enters through the opening in the front of your eye (the iris) and passes through a crystalline lens. The lens focuses the light into an image that falls on your retina (the inside of the back of your eye). When an image falls on the retina, nerve cells send signals to your brain which are interpreted to create an image.