Abstract

Light does not penetrate far in a very dense fog, and the problem of safe navigation through fog cannot be entirely solved by the use of light signals. In harbor, canal and river navigation it is common practice to indicate the course by means of signal lights so placed as to provide clear visibility and directional guidance in fair weather. The usefulness of such systems of signal lights can readily be extended to include less favorable weather conditions, such as mist, rain, snow and even fog of appreciable density, by proper spacing and design of the units to insure high efficiency and proper light distribution within the angle of view. The principle of varying the lamp voltage to reduce or increase the beam intensity in accordance with weather conditions is suggested.

© 1935 Optical Society of America

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