The complementary-color headlighting system is based upon the use of differentiated light, that is, light having different wave-lengths. Each head-lamp is oval and contains two paraboloid reflectors, one emitting light through an orange glass filter, the other through one of blue glass. While driving at night, the driver looks through a viewing-filter of transparent glass of the same color as that of the headlight which is in use. The viewing-filters are arranged so that whenever one is used, the headlight of the same color is automatically turned on. When the headlights are not in use, the filters are held in the filter-box and are out of sight. It is the intention that cars traveling in a general direction, say north and east, shall use the blue light; that those traveling south and west shall use the orange light. Each viewing-filter is transparent to the light that is thrown on the road by the headlights of the same car but is opaque to the lights of approaching cars. The result is that ample illumination is provided for perfect visibility but no glaring lights from approaching cars can reach the eyes of the drivers.
Selection of the proper headlight is simplified by the fact that the color of the headlights is controlled by the viewing-filter used and a driver must protect oncoming drivers to obtain protection himself. Conformity is necessary to obtain personal safety.
When meeting cars that are unequipped with the new system, the viewing-filter allows only about 25 per cent of the incident white light to pass, and unequipped cars are at no disadvantage because the luminous flux with the new system is not more than that supplied by the standard lamps in use at present.
Tests of the apparent brightness of a target placed 3 ft. to the right of the head-lamps at a distance of 70 ft. show that, in order to have the same target equally visible under both systems, the ratio of its apparent brightness in the old and in the new system must be as 25 is to 1.
Red danger-signals are visible through either viewing-filter and are distinguishable from lights of other colors, such as orange, yellow, white, green, or blue.
As color blindness is not a lack of the sensation of luminosity but of hue sensation in certain portions of the spectrum, a person who could not distinguish a red light while using the complementary-color system could not do so while using the present system.
Among other topics given consideration are the danger due to a low distribution of light, especially when encountering pedestrians on the road at night; the economic and sales factors involved in a change of headlighting system; the general subject of visibility and the limitations of the eye; the danger arising from the dimming of headlights due to the time required for the “threshold” to drop; the relative proportion of deaths and accidents caused by conditions of poor visibility; and the sales advantage offered by the increased comfort and pleasure of night driving with the new system.
In conclusion, a comparison is made between the use of undifferentiated headlighting and a radio broadcasting station that is allowed to broadcast over the whole range of wave-lengths; and stress is laid on the point that no consideration of inconvenience or trivial increase of cost can justify the continuance of the present system with its record of accidents and fatalities.