Citation

Howard J, Finch DM. Highw. Res. Board bull. 1960; 255: 146-157.

Copyright

(Copyright © 1960, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

Previous investigations of the visual characteristics of flashing light sources, for the most part, have been made at low-energy levels at or near a visual threshold by means of extended sources. Although the results of these investigations have proved useful, they are not directly applicable to the design of portable battery-operated warning lights where conditions are somewhat different. These divices are usually first seen as nearby point sources under suprathreshold conditions. New data have been developed which relate to the important physical characteristics, such as flash duration and wave form, that directly affect the perceptual clues provided by such warning devices. The effect of duration and wave form on the effective intensity of point sources of flash energies of 0.1 candlepower-seconds (red light) has been investigated by performing intensity matches between two modulated sources, one of which has a fixed duration and peak intensity. At this flash energy, which was chosen as being significantly above a visual threshold for a dark-adapted eye and as being readily obtainable by currently manufactured devices, flashes that have durations longer than 50 milliseconds require more energy to have an equal visual effect than flashes of shorter duration. This result is highly important to the conservation of battery energy. Other factors that influence the design of battery-operated units (for example, flash rate, flash energy, and placement of units) are discussed.