From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Article from 'The Motor' magazine about comprehensive and instructive tests of modern anti-glare devices.
| Identifier | ExFiles\Box 61a\1\ scan0063 | |
| Date | 31th March 1920 | |
| The Motor 412 March 31, 1920. CAN DAZZLE BE DESTROYED? Comprehensive and Instructive Tests of Modern Anti-glare Devices. AS we have frequently pointed out in these pages, the all-round increase in the importance of motor transport and the greater numbers of cars which are now using our roads calls for attention to the problem of preventing all road users from being blinded by powerful headlights. We have at various times illustrated and described devices which claim to attain this end. On Monday, last week, we were present at an interesting and instructive series of tests which were carried out by Messrs. C. A.{Mr Adams} Vandervell. In the first place, we should like to express our appreciation of the thorough and disinterested way in which the demonstration was conducted. Messrs. Vandervell are, at the present time, not manufacturing any special form of lens, and those present were invited candidly to give their unbiassed opinions, and no distinction was made between any of the patterns. On a lonely stretch of road running through Oxshott Woods, near Esher, a distance of 50 yards was paced out. A stand on which any type of head-lamp could be mounted at a normal height from the road was levelled up and put into position, while at the other end of the 50-yard stretch a post bearing three white discs at different heights from the road was placed, in order that photometric readings of the intensity of the light projected at this distance might be measured. In the majority of cases the anti-dazzle devices were fitted to standard C.A.V. head-lamps of 10 ins. diameter, a parabolic reflector and a 32 c.p. bulb being used. Only one lamp was used in all cases except that of the Lucas Diffusa lens, which was fitted to a car and seen under normal running conditions. This particular device was the first to be tried, and it was easily seen that the etched “Diffusa” glass improved the visibility from the driver’s point of view, gave a much more even spread of light in the area illuminated, while the glare and hard blinding rays were greatly diminished. The Macbeth lens, which consists of a serrated glass front cut in a scientific manner and provided with a green visor or top shade, proved effective as an anti-dazzle device at a distance of 15 yards. Beyond this the light was certainly thrown on to the road, although when in the direct beam the blinding effect could easily be noticed at a normal height. This latter tendency, however, was found with all the patterns. At a distance of 50 yards the light was certainly very little better than would be the case with an open lamp. A front which was fitted with horizontal metal shutters had little or no effect at a distance, although the top rays which caused glare were cut out at a distance of 12 yards from the lamp. The next types to be tried were the Salsbury devices. These consist of horizontal strips of glass clamped together to form a circular front. The top side of each piece of glass is ground so that the light is to some extent thrown down on to the road. These fronts were quite effective. There was no glare up to 20 yards away from the lamp, while the intensity of the light projected did not seem to be greatly diminished. Road illumination was good, although, as we say, at a distance the glare was present. A Holophane lens, which has already gained considerable popularity, was then tried. This, in our opinion, was very good. It can be seen from the illustration that it consists of a prismatic front, on the back of which a horizontal piece of glass is fixed. The beam of light was kept low, while even at a distance the glare was certainly reduced. At the same time, the light was concentrated, and, if anything, the driving visibility was improved. Another type, consisting of horizontal and annular strips of metal, proved ineffective, but a Liberty lens kept the light down on the road, and to some extent minimized or softened the glare. The Lucid front certainly kept the beam in a straight line and had an anti-dazzle effect up to 17 yards. Beyond this distance practically no difference was noticed, while light was reduced. It seems impossible to arrive at a compromise between a light which is powerful enough for fast driving and which does not dazzle approaching motorists or pedestrians at a distance. Such lenses as the Holophane, Liberty, and Lucid certainly improve matters in that sufficient distance is provided between passing cars during which the drivers are immune from dazzle. The Lucas Diffusa augments the visibility and decreases dazzle close up, but even in this case a certain amount of dazzle at a distance seems inevitable. Photo on the left shows the effect without an anti-dazzle device, that on the right shows effect with an anti-dazzle device. The camera was the same distance away from the lamp in both exposures. | ||