An Evaluation of the Hypothesis That Laser Light is More Conspicuous Than Incandescent Light
COAST GUARD RESEARCH AND DEVELOPMENT CENTER GROTON CT
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It has been thought that laser aids to navigation might appear more conspicuous than aids employing conventional light sources. Two experiments rigorously tested the hypothesis that laser light is more conspicuous than incandescent light. Incandescent and Helium Neon laser sources were optically filtered and adjusted to present the same illuminance and color to distant observers. Thirty-seven observers viewed 60 random presentations 2 source types, 2 illuminance levels from a distance of 1500 yards. Group correct source discrimination percentages were 52.6 and 55.2 for the low and high illuminance levels, respectively. The experiment was repeated indoors at higher illuminances with resultant group correct source discrimination percentages of 57, 67.5, and 66 for the low, medium, and high illuminances, respectively. It was concluded that at practical design illuminance levels, no significant conspicuity advantage would be gained by replacing existing navigational aids with laser aids-to-navigation. Calculations show that a significant conspicuity advantage is likely to be obtained if the mariner uses a narrow bandpass filter 3-10 nm centered at the laser wavelength. The illuminance from the laser will be relatively unaffected, while the illuminances from all background lights will be dramatically diminished. An additional section compares the electrical efficiency of a standard Coast Guard FA-240 range light with a laser aid configured for the same application. For equal input power, the FA-240 is shown to produce 10 times the luminous intensity of the laser aid.
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