NOTES FOR THE OWNERDRIVER

Nelson Evening Mail, Volume LXIII, 13 July 1929, Page 9

NOTES FOR THE OWNERDRIVER

;; , HEADLIGHT GLARE THE DAZZLE PROBLEM The solution of tlie glare-problem from automobile headlights is not a question of optics, but 0110 of common courtesy and practical sense. The problem is one which is always with us. Fifteen or 20 years ago very few people motored by night, to a greater extent than was compulsory. Even in 1009, electrical lighting was an “extra” on a majority of cars. The standardisation of electric lighting and starting, only came into vogue about 15 years ago. Up till then most cars were equipped with oil side lamps, and acetylene liead-lamps. The more “swagger” cars next had battery-fed electrical .sidelamps, and then Chas. Vandervell, in

England, the Rotax-Leitner people in Germany. and the Ducellier-Bleriot company in France came forward with lighting dynamos. From that moment there was a dazzle problem. And to-day with cars used from sun-

rise to sunrise by all sorts and conditions of people, the dazzle problem is just as acute in summer as in winter. because nobody any longer thinks ! t remarkable fn drive through the whole of tlie night. Many car owners, no doubt, have some knowledge of optics, of the nature, phenomena, projection, reflection and refraction of light and therefore can appreciate the root cause of the head-light glare; which is responsible for a certain percentage of accidents. The parabolic reflector of an ordinary head-lamp is so designed, optically, as to collect, light-rays from the incandescent filament, of the bulb, focus or concentrate them centrally, and then throw' them forward from a pin-point in sucli wise that they will form a fan-like beam of light which broadens from that focus pin-point to infinity. Tliis broadening' is necessary to diffusion. The ideal driving light is one which will; stream forth in a fanshaped beam, so illuminating the maximum possible amount of space ahead of the car.

Unhappily, however, for the people met on the road (whether they be other motorists, horse-drivers, cyclists pr pedestrians) these parabolic reflectors are a little too efficient, with the result that the more forward ends of the two beams of light are diffused not only laterally—by which is meant from side to side of the space ahead of the car, and downwardly, on to the road—but

also upwardly to such a degree that some of the upward reaching rays shine into the eyes of approaching roadusers. It is claimed that this inconvenience can be prevented by allowing only the upper, half of the surface of the reflector to function, thus permitting no rays of light to travel upwardly beyond the level of the top of the lamp itself. Tins is accomplished by the use of double-filament lamps.

In Continental countries where there is in operation legislation rigidly forbidding the use of glaring liead-lamps, the double-filament solution of the problem is that most numerously employed, and as European opticians (in the broader, more scientific sense of tlie word) are quite as advanced as British or American, it may be fairly assumed that the double-filament lamp is the'-most efficient and most satisfactory solution of the common problem* Merely to “clip” head-lamps, it is said, is not enough, because the act of “clipping” robs the light of its diffusion and immediately in front of the car with “dipped” head-lamps is a patch of concentrated light, hut outside that patch all is blackness. With the two-filament lamp,, when the main filament is switched out of action, all the light used comes from the minor or anti-dazzle filament, beneath which is a spoon-like mirrorsurfaced metal screen, whose effect is to throw the light from the anti-dazzle filament on to the upper portion only of the main reflector’s surface, which latter throws it downward, but does so without any reduced diffusion, so that instead of the concentrated patch - of “solid” light which is all that one; gets with dipping head-lamps, one has a nicely “fanned” light extending very widely, but none of it rising above .the waist-height of an average pedestrian, or above a cyclist’s handle-bars. The two-filament lamp is operated by the foot, by depressing a switch, placed slightly to the left of the clutch pedal. This type of lamp is already on the market.