Demos: 7A-24 Light Pipes

Twisted glass and plastic rods with polished ends are used to demonstrate the action of light pipes (guides).

Directions: A variety of guides is available. Dim the room lights and place the laser so that the beam strikes one (polished) end of the guide at near normal incidence. The other end should face the class. To make the exit beam more visible to the whole class, place a sheet of white paper in the path. There will be a visible concentration of light on the paper.

Suggestions for Presentation: An overhead transparency accompanies this demonstration, showing the light path inside the guide. You should point out that if these guides were perfect, the light would not be visible at all inside the guide. However, the guides have internal blemishes as well as scratches on the walls, causing some of the light to exit the pipe along the way.

Possibly the staff will be able to provide some consumer “light pipes,” such as novelty lamps and toys. These are reasonably good pipes and most of the light is seen only at the ends.

Applications: Fiber optics. Cameras, light transmission, etc.

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