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"Standard Lamp Design the Answer to Dazzle"
Page 110
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Road Research Laboratory's Investigations into Problem of Glare : Special Lamps for Goods Vehicles Proposed: Need for Proper Lamp Maintenance
4‘ 0 achieve as high a standard
of visibility as can reasonably be expected, it is necessary first of all to choose a headlight beam of good design. But the choice is not unique; quite a range of designs give very similar visibility. The standard of performance of which they are capable will not, however, be obtained in practice unless one design only is in use at any given time, and unless the lamps are correctly aimed and maintained, so that there is substantial uniformity of lighting on all vehicles."
Dr. W. H. Glanville, Director of Road Research, makes this observation in "Vehicle Headlighting: Visibility and Glare," a new publication by the Stationery Office at 2s. It contains the Road Research Laboratory's findings on the headlamp-dazzle problem.
"Drivers with good lamps," states the book, " find themselves dazzled by about 15 per cent. of the vehicles that they meet coming towards them. Drivers who do not make use of their dippers are comparatively few."
Three Requirements There were three requirements for the ideal beam. First, it should reveal objects far enough away for the driver to be able, if necessary, to avoid them. It should also reveal the kerb to enable the driver to judge his distance from it or the centre of the road. Thirdly, it should not dazzle the approaching driver. The first and third necessity conflicted and made the solution of the dazzle problem difficult.
The USA. and most countries ot Western Europe had gone farther than Britain in setting standards to which headlamp beams must conform, but they were not satisfied. Trials had been carried out since the war in an attempt to find a beam which would be Universally acceptable, and development was still proceeding.
The tests by the Laboratory revealed that all beams were judged to be more dazzling on wet roads than on dry ones. Wide beams which were pleasant on dry roads were found to be glaring on wet ones, yet visibility on the road was much the same whether it was wet or dry.
About 16 per cent, of pre-war vehicles had beams so diffuse that their aim could not be measured. The newer flush-fitting lamps had only about half the scatter in vertical aim of older types, but pass lamps were likely to be much more offensive than headlamps.
Lamps deteriorated mainly because of corrosion of the reflectors, or dirty F20 contacts which reduced the applied voltage. Lamps on vehicles registered in 1949 or later had a markedly higher average intensity than those of older vehicles, and did not appear to have deteriorated greatly.
The book gives a table which shows the amount of tilt produced with different types of goods vehicle by the imposition of a load. Loads were placed at the front of each type and at the rear, and the difference in vertical aim of the lamps was measured. For a Thames 10-cwt. van the variation in angle was 2'; a Leyland 5-tonner, 3.4'; a Bedford 3-tonner and an A.E.C. Matador, 2"; and a Thames 4-ton tipper, 2.7'.
Easy Adjustment
The less the performance of a lamp depended upon careful adjustment by the user, the better results were likely to be. A lamp, if not of the sealedbeam variety, should be fitted with a pre-focus bulb, and an acceptable method of fixing a lamp would allow smooth and easy adjustment of aim, which should not alter during any locking process.
The arrangement now used on many lamps, in which the aim was adjusted by turning three screws, was probably satisfactory; the older system of a universal joint and locknut not so. It
was desirable to devise a variation the three-screw mounting, in which screw was brought to the front of lamp, to be readily accessible setting, like the waveband switch c radio, to a number of marked positi to compensate for the tilt because a particular state of loading.
If the headlamps of a lorry si aimed when the vehicle was empty, t would be extremely glaring when it laden. Conversely, if they were air • when the vehicle was laden, they we
• be very poor when it was empty; driver would be dazzled by oi vehicles, and the horizontal inten would be reduced by 40 per cent.
The system of altering the adj ment suggested, however, might be to abuse, and the book proposes headlamps for lorries be of a t different from those fitted to cars. T should have a lower horizontal in sity, because the driver of a h vehicle, being high up, was subjec to less dazzle than the driver of a The cut-off of a lorry lamp might less sharp so that the beam would less affected by changes of tilt. S lamps might be more glaring and efficient than the car type when te: in the ordinary way, but under won!. conditions might be more satisfacto The difficulty of changes of because of loading could also be o come were it possible to Mount lamps on some part of the struci which did not tilt; alternatively, a c. pensating linkage might be devisei
It was suggested that the centres headlamps should be between 2 ft. z and 3 ft. from the ground. If the of one design of lamp were succ fully introduced for all vehicles mz facture-d after a certain date, question would arise as to what slit be done about vehicles already on road not using the new pattern.. It wc be desirable to improve the old la rather than to await their eventual appearance from the road, but w headlamps were replaced, the pattern should he fitted.
Special Equipment
Some form of control would necessary, but the police would req special equipment to check lights. number of instruments for measu headlight aiming had been examine( the Laboratory, but none was jut entirely suitable.
Other ways of combating the da problem lay in improving street Ii ing, but polarized light held out best promise. If it were to be hi. efficient for the driver, however would be extremely dazzling for un tected road users, particularly cycl
At the Commercial Motor Show, Department of Scientific and Indus Research will have an exhibit Stand 15 devoted to the dazzle prob A panoramic model will show a ty/ stretch of open road at night, as from a driver's seat. A sequenci familiar situations leading to dazzle be demonstrated with actual headlit misaimed or otherwise unsatisfacl