HEAD-LAMP LIGHT-CHARACTERISTICS AND DISTRIBUTION 260022
Subsequent to reviewing the circumstances responsible for the present complicated situation existing with respect to satisfactory automobile-headlighting, the author says that headlights glare if they are adjusted for range and that, when adjusted for non-glare, they have no range; hence, careful tests were made on a number of the best types of approved headlight and lens in use. The units were set-up in pairs, in operating position as to height and interval and were tested at a range of 100 ft. with a 1-m. (39.37-in.) hemisphere having an aperture 21 in. square, corresponding to 1 deg. at 100 ft. All the lamps were held at proper current-value throughout the tests, and it was demonstrated by the tests that the reflectors of the parabolic type and others of similar characteristics that have proved to be unsatisfactory during many years past must be abandoned.
Regarding the so-called “hot-spot” of light on the road to facilitate high-speed driving and the tendency toward such practice lately evidenced, the author sees no reason that anything beyond 20,000 cp., maximum, is required, and says that half this candlepower would be sufficient in a well-balanced light. The main light-beam should have a good lateral spread so that it will cover for a considerable distance not only the road but also the ditches, with reasonable depth so as to carry a gradually diminishing illumination to within say 20 ft. of the car, and should illuminate the wheels and the running-board of the approaching car clearly at a distance of at least 200 ft. without projecting any direct rays into the eyes of the approaching driver.
Commenting upon fog penetration, the practice of “dimming,” tilting reflectors, and two-filament lamps, the author says that headlights of the future should have range without glare and should not require tilting, dimming or any other form of manual operation. He believes that the two-filament lamp will do much to improve the present situation, states specifications for improved headlights and discusses the tests and the illustrations.