PURPOSE: To demonstrate how color TV equipment derives its color, and to illustrate a defect in handling of saturated colors such as spectra.

DESCRIPTION: A prism white light spectrum, demonstration N1-01: PRISMATIC SPECTRUM OF WHITE LIGHT - POINT SOURCE, is viewed by a color minicam and displayed by a color video projector adjacent to the original spectrum. The spectrum produced by the projector has three bands of uniform color: red, green, and blue, separated by small gaps.

This effect creates a problem in producing photographs and videos of line spectra or other types of highly saturated colors. Fortunately, most color in the real world contains wide bands or continuous wavelengths, and is therefore handled reasonably accurately by video.

An example of this effect in film is the color slide series THE LIGHTS ON CAMPUS: A STUDY OF ATOMIC SPECTRA, distributed by the AAPT. The hue of the continuous spectra does not change continuously throughout the spectrum, but rather the spectrum on film is formed from three uniformly colored RGB segments separated by small gaps.

SUGGESTIONS: Use low brightness and contrast to avoid overlap of bands.


EQUIPMENT: Prism spectrum from demonstration N1-01, minicam, and color video projector.

SETUP TIME: 10 min.

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