Experimental Study on Recognizability of Ship Lights at Night

Abstract

The ship light display is regulated for ship collision prevention in accordance with international rules. Whether ship lights are adequately recognizable or not is a vitally serious problem as it has direct influence on prevention of ship collision. A study was made this time on the recognizability of ship lights. 1) Experiment on the chromatic threshold of a spot luminescent source. The result proves that the average chromatic threshold of five subjects is 6.57×10^<-8> l_x for white, 2.03×10^<-8> l_x, for red, and 10.12×10^<-8> l_x for green, respectively. Provided, however, that selection was made from color filters with the standard chromaticity commonly adopted by ships. Where the ship-light recognition distance was calculated, based on this experimental result, and on the assumption that the electric bulb of a ships light is 40 Watt, the respective distances were obtained as being 5〜7.2 sea-miles for an incandescent lamp, 4〜5 sea-miles for a red lamp, and 2.3〜2.8 sea-miles for a green lamp under very clear atmospheric complying with the atmospheric conditions stipulated by the international visibility standard. Attention must be directed to the fact that it is especially difficult to recognize a green light. 2) Experiment on the recognizability of ship lights classified according to the respective patterns. The ship light patterns were selected in conformance to concrete examples stipulated by the ship collision preventive law. In I group, a white lamp was combined with a red lamp while in II group, a white lamp or a red lamp was combined with a green lamp and to the subjects were made to recognize these patterns while experimentally performing the simulation. In the case of the II group in which a green lamp is combined, the result proves that it is difficult for the subjects to recognize the green lamp, remarkably reducing the recogniton rate.