PURPOSE: To illustrate the optics of an optically programmed traffic signal.
DESCRIPTION: The overhead projector platform is covered by two color filters, arranged so that the left section is green and the right section is red, and the entire projector except the exit lens is covered by a box. When the lens is aimed at the class, the red and the green areas are focused such that any student sees either red or green.
Optically programmed traffic signals make use of Fresnel lenses in a similar type of optical system to allow the light to be seen only in certain lanes of traffic. Optically programmed traffic signals can be identified because they should be rigidly attached to some support and they are rather soft colors (not bright like direct lights).
REFERENCES: (PIRA unknown.) See Demonstration Reference File for lots of information about production and installation of optically programmed traffic signals.
EQUIPMENT: Optically programmed traffic signal model.
SETUP TIME: 5 min.
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