Lights Inaccurate and Inadequate
Page 65
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Loudon Conference Reveals the Many Problems for Solution in Providing Increased Safety on the Roads pROBLEMS awaiting solution in road and vehicle lighting were discussed at a Conference on Vehicle and Road Lighting held by the Institution of Mechanical Engineers (Automobile Division) on Tuesday.
All aspects of the subject were • covered in four papers, which, being complementary to one another, inevitably introduced duplication of thought, but there was unanimity as to the serious problem whieh safe lighting presented. .
From an analysis of records of two-vehicle accidents compiled from October to December, 1949, it could be concluded that the pre-war vehicle, with its poor rear light, was roughly• six times as likely, as a post-war vehicle to
• be hit at the rear. This evidence was quoted by 'Mr. K. N. Chandler. B.Sc., Ph.D., and Mr. J.A. Reid, both of the Department of Scientific and Industrial Research and Mr. K. J. Jones, B.Sc., of joseph Lucas (Electrical), Ltd., in their paper,. " Rear Lights and• R eflectors."
Heavy Cost of Accidents
It had been estimated, they said, that accidents which could have been avoided had good rear lights been in use, had cost the country about E2m. per year. It had been found that a normally efficient rear Tight, if not kept clean, would suffer in intensity by as much as 50 per cent. over a period of a week in bad weather.
Judgment of distance was affected both by the degree of intensity of a light or by its height from the ground. The brighter the light the nearer it appeared to be, and the higher it was from the ground the farther it seemed to be away.
Whilst two lights placed close together did not aid the judgment of distance, there was a significant improvement when the lights were 2 ft. or 4 ft, apart,
Rear Lights versus Reflectors
Experiments had shown that a reflector was not generally visible at such large distances as a rear light, but once it was visible it " came up" more rapidly than a rear light. This was explained by the fact that by halving its distance away, a rear light appeared four times as bright, whereas a reflector appeared 16 times as bright. It was also shown that mist interfered more with reflectors than with rear lights.
A simple test for a reflector was to place several different types at a distance of about 20 ft. and direct on to them a beam of light from an electric torch with the torch held about 1 in. to 1 in. from one eye. The best reflector was the one which appeared brightest. If the torch were held near the chin, the poorer reflectors might appear brighter than the better ones. "Street Lighting Performance" was the subject of the paper read by Mr. 11, -R. Ruff, B.Sc.(Eng.), M.I.E.E., and Mr. G. K. Lambert, B.Se.(Eng.), A.M.I.E.E., both of British ThomsonHouston Co., Ltd.
The question whether headlights should be used in built-up areas was a contentious one, they said, and one of the concerns of the street-lighting engineer was to bring lighting to such a standard that safety was assured without headlights being employed.
The objectives aimed for were to enable a driver with normal vision to follow his route and to perceive any object on the road without aid from his headlights. He also needed to see the kerbs at both sides of the road and for a considerable distance ahead.
It was important to he able to see objects in silhouette in lighted streets,
but this was not -the whole story.
Reversed silhouettes might be valuable in positions just beyond a street lamp, but contrasts with objects the size of a pedestrian 300 ft. away were relatively unimportant.
Function of Road Surface
As silhouette vision was. given by the light reflected from the road, the question of road surfacing was material. The more light it reflected the better was visibility, but this characteristic might have to be subordinated in order to maintain high skid resistance. • For this reason, modern roads had rough surfaces. They were also generally dark, and on dry roads the brightness produced today was lower than on many of the surfaces common in the 1930s.
Some• modern road surfaces did not enable the maximum road brightness to be obtained from the higher-angle beam system and the most satisfactory compromise appeared to lie with a mediumangle beam with carefully limited light intensities above the beam.
Despite the complete revolution in transport which had taken place in the past 50 years, the head lamp still remained only an optional extra in Britain. This significant fact was underlined by Mr. J. H. Nelson, B.Sc., Ph.D., chief lighting engineer, Joseph Lucas (Electrical), Ltd., in his paper, " Design • and Use of Head-lamp Meeting Beams."
On the Continent, he said, the dazzle problem had been met by the use of a special bulb which was invented in 1920. This bulb, in conjunction with a metal screen placed below an axial filament, produced a beam of light having a short horizontal cut-off. This system was universal in Europe, 'although it had been abandoned in this country.
It would probably be true to say, said Mr. Nelson, that in Germany there was more concern 'about visibility, evenssat the expense of glare, whilst at the other end of the scale France was convinced of the paramount importance of reducing uncomfortable glare even at the expense of visibility.
Since 1937, the use of head lamps giving a yellow beam had been obliga tory in France. Nevertheless, the vast majority of tests comparing yellow light with white light under otherwise identical conditions had failed to show any significant advantage in -favour of yellow light.
In appreciation tests, however, drivers in general stated that when driving with yellow lights and meeting identical lights, they experienced less glare than when driving with white lights and
meeting white lights. Despite-this, they quite definitely, stated that they preferred to drive with white lights.
It was, however, possible to say categorically that no great improvement in visibility distance was obtainable by the use of yellow filters.
Built-in Lamps Stable
In the design of the builf-in head lamp, much more care was taken to ensure that accurate aiming was possible, and that the lamp, once aimed, remained stable. Even so, correct aiming on any vehicle would depend on hazy its springs settled in service, the loft the state of the tyres and so on. It was, therefore, important to have the head lamps inspected and properly set from time to time.
If only for the reason that a pedestrian would rarely cross in front' of a vehicle having its headlights on, Mr. Nelson thought that there was a strong case for adopting this practice in built-up areas.
In his paper, "The Performance of Head-lamp Meeting Beams," Mr. G. Grime, 0.B.E., M.Sc., of the Department of Scientific a n d Industrial Research, said that the_ control of the aim and intensity of meeting beams in use on the road was the most difficult, as well as the most necessary, part of the procedure for improving vehicle lighting.
Controlling Aim
Three methods had been considered: (1) By having testing gear available in garages, (2) by voluntary vehicle inspection, and (3) by compulsory vehicle inspection.
A substantial improvement in visibility and dazzle prevention was possible with present equipment if means could be found to improve aim and to restore or replace lamps that had deteriorated. No change of lamp design alone would achieve a big improvement, added Mr. Grime, and no new lamp design was necessary or desirable at present.