One, Two and Spot
Page 27
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WITH the increasing speed, and possibly gross weight too, of heavy gopds vehicles, illumination of the road ahead at night becomes steadily more vital. In the immediate post-war days headlamps were certainly unsatisfactory, but design has come a long way since then. What is the position today? More important, what is the outlook for tomorrow—and the day after that?
Those questions are answered in an article by The Commercial Motor technical editor on page 576 of this issue.
In the process of answering those and many other related questions the author of this article arrived at the possibility that, for some opera: tional purposes, the perpetual use of long-range driving lamps and spot-lamps instead of the main lighting equipment may, in the next five years, become a thing of the past. Headlamp design should, without unnecessarily dazzling oncoming traffic, provide sufficient forward light in normal conditions. There will always, of course, be a need for auxiliary lights on a heavy vehicle, but they may not need to be called upon in preference to headlamps.
Whether dual or single headlamp sets will be used seems to be an open question. Commercial vehicle designers were ahead of their private car cousins in the use of dual headlamp systems on both goods and passenger vehicles. At the moment, two 5i-in. lamps are used for each pair. A mixed system of one 5i-in. and one normal 7-in, unit on each pair was shown on a private car at Earls Court last month. A firm forecast is that a dual 7-in, double-filament system will soon become available. With this latter system, its power on dipped beam raised to equal that of the present 5i-in. units, the lighting efficiency should be put up by some 20 per cent.
The alternative to dual headlamp 'equipment is the single headlamp set. The all-glass, sealed-beam unit has increased lighting output from 42 W. on main beam and 36 W. on dipped beam (the efficiency of lamps 15 years ago) to 60 W. and 45 W., respectively.
Advances with other aspects of headlamp design, such as with the all-important lens, and with the reflector material, all add up to an impressive record of achievement by British manufacturers. Whether using single or dual headlamps, and with auxiliary lamps for special conditions, British commercial vehicles have a bright future ahead.