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USE YOUR HEADS

24th November 1961
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Page 58, 24th November 1961 — USE YOUR HEADS
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Improvements in British Headlamp Systems are in Keeping with Increased Road Speeds ; Accurate Manufacture Can Reduce Dazzle

By John F. Moon, A.M.I.R.T.E.

ON noticeable feature of any night drive down a British

main road these days is the increasing number_ of heavy-vehicle drivers who seem to prefer to use their vehicle headlamps—usually dipped—rather than the various types of auxiliary driving lamps which, until recently, formed most drivers' only acceptable form of night-driving illumination.

Such auxiliary lamps are still used in appreciable numbers, of course, to -the detriment of oncoming traffic (particularly private cars), whose drivers are inevitably dazzled by the badly aimed, wavering, near-horizontal beams cast by such devices, which frequently appear to be mounted on springs to increase the dazzle effect.

Fortunately, the headlamps fitted on commercial vehicles as standard equipment have improved by leaps and bounds over the course of the last decade or so, and it could well be that within the next five years perpetual use of spotlamps and long-range driving lamps will become a thing of the past, although there will probably always be need for the occasional use of such lights to supplement the headlamps by giving added illumination a long way ahead of the vehicle. Special fog lamps giving a widespread, flat-topped beam will always be needed; of course.

Overcoming Inadequacy

The vogue for spotlamps really stemmed from the inadequacy of the original-equipment headlamps available to vehicle manufacturers before, during and immediately after the last war. The headlamp systems in use in those days usually had the near-side lamp permanently tilted downwards by about 2, and " dipping " consisted merely' of extinguishing the straight-ahead, off-side lamp.

No one could claim that this gave satisfactory illumination either when the system was on main beam or when it was dipped, and particularly in the latter condition dazzle to oncoming vehicles was a problem. Many variations of this same basic theme were tried, including one well-known system in which the near-side lamp had a pivoted reflector which was tilted downwards by a solenoid when the dip switch was operated, the off-side lamp being simultaneou'sly extinguished.

Double-dipping Arrive3 Inadequate as this type of equipment Was for British conditions, it was almost completely unacceptable in overseas territories, and the resurgence of the British automotive industry's export efforts soon after the end of the War made it essential that •a more satisfactory type of headlamp bedeveloped. The result was the original ".double dipping" system, in which each lamp had doublefilament bulbs, one filament to give a main beam and the other to give a dipped beam in the case of both lamps.

The improved illumination given by both beams was remarkable, but British drivers did not take kindly to the idea of the off-side lamp staying illuminated—albeit with the beam dipped—in the face of oncoming traffic, and those drivers who were "pioneering enough to make use of their increased illumination with dipped lamps invariably found themselves being flashed at angrily by their oncoming brethren. In self defence the inevitable auxiliary lamp was reverted to, so as far as the vast majority of the motoring public was concerned the dazzle problem remained.

These original double-dipping lamps were made in 8-, 9and 10-in.-diameter sizes -and had silvered reflectors, which were in themselves another source of trouble because of the " open " construction of the lamp. This type of assembly made it relatively easy for the driver to remove the headlamp rim and lens and so, as he thought, clean the

eflector, although actually all he was doing was removing he silvering and therefore reducing the light output.

In 1950 the original "sealed" type of double-dipping amp with block lens was introduced by Joseph Lucas, Ltd., vho supply most of the headlamps for the British vehicle ndustry in conjunction with their associated company, -.AV., Ltd., whose main field lies with heavy vehicles. This 1950 lamp, which conformed to International standards by having a nominal diameter of 7 in., was progressive for its use of .a pre-focus bulb, access to which was through the back of the reflector, the rim and lens being sealed to the metal reflector, so that . its surface -could not be marred by the effects of too much over-enthusiastic cleaning.

As with the earlier types of double-dipping system, a two-filament bulb was used to provide main and dipped beams, and the method of bulb location ensured a higher degree of filament alignment relative to the reflector than had been obtained previously. The silvered brass reflector of this lamp was soon superseded by an aluminized steel reflector, and this type of lamp is still in common use in Britain, only flaw being gradually supplanted by more recent designs, as detailed later.

The change from brass to steel for the reflector material is significant. For one thing a steel reflector is cheaper than a brass one, and silver-plating brass is a more costly process than aluminizing steel. Furthermore, comparing the finished products the aluminized-steel reflector affords greater reflectivity, and stays bright because there is no lacquer film (which browns with age) to obscure the polished surface, silvered reflectors having been protegted with such a lacquer.

The improvements introduced during this period with respect to the reflectors and bulbs of headlamps were paralleled by equal progress in the design of the lamp lenses. Originally, lenses were merely flat, acid-etched sheets of glass, which had the effect of diffusing the beam. Next came moulded glasses with vertical ribs which gave some measure of horizontal beam control, in that the beam was spread over the road surface, but no vertical control. '

The vertical ribs were retained for the neXt move, but prisms were incorporated with the ribs to give a measure of vertical beam control. With the advent of twinfilament bulbs the block lens was developed to give an even spread of light all over the road, although even this was a compromise in that one lens had to control both main and dipped beams.

This basic type of block lens is still used on all the latest types of lamp, and it is perhaps not generally recognized how important the lens is. Its characteristics define-to a considerable extent the type of beam emitted and its direction: for instance, identical lamps can be made to dip to either left or right, according to the type of lens installed, and to use " left-hand dipping" bulbs behind "right-hand dipping" lenses is a poor compromise, although obviously the cheapest expedient for vehicles continually operating both in Britain and on the Continent.

Like all designers, Joseph Lucas' back-room boys were • stillnot satisfied, with the result that the metal-backed sealed unit is now gradually being replaced by.the allglass, sealed-beam lamp. The main reason for the development of this type was to ensure much more accurate positioning of the filaments relative to the reflector, the reflectivity itself being almost the same as that of the pre-focus-bulb lamp except that the reflector area is slightly greater because of the absence of a hole in the centre of the reflector where the bulb fitting of the earlier type is located.

The sealed-beam lamp has been criticized on the grounds that failure of one filament involves replacement of the complete unit, because the all-glass, sealed lamp is, in effect, a large bulb and must be more expensive to replace than the old type of pre-focused bulb. However, the completely sealed lamp promises to have a better life 'than that of a pre-focused bulb, and in any case the easily recognized improvement in the quality of the light emitted is in itself well worth the extra cost of replacement.

The 7-in., all-glass lamp has a 60W. main beam and a 45W. dipped beam (at 12.8v.), compared with 55W. and 44W. respectively given by the metal-backed lamp with pre-focused bulb. These figures alone show the progress that has been made since the war, lamps being produced about 15 years ago giving 42W. on main beam and 36W. when dipped, these figures gradually rising to 50W. and 40W. respectively up to the introduction of the pre-focusedmilb unit The all-glass lamp has an aluminized glass reflector and :he complete unit is gas filled after precision location of .he two filaments. Thus the reflecting surface is permalently protected from both the weather and inquisitive ingers, and since there is no separate bulb which could )1acken with age, high light output is maintained throughnit the life of the lamp.

A filament shield is incorporated to reduce the upward ;pread of the beam, and this is found to be of advantage n misty or hazy conditions, whilst—and this is the main )oint of the design—the control that can be exercised over he location of the filaments ensures both concentration and listribution of the components of the beam exactly where hey are needed, under both dipped and main-beam :onditions. .

More Light, Less Glare Thus, on main beam, the range of vision is greater than hat obtainable with the pre-focused-bulb lamp, whilst when lipped the beam gives a greater range along the near-side ...erb, improved distribution immediately in front of the 'chicle, and less glaring light above the horizontal to the di-side, and therefore less annoyance to oncoming drivers. The advent of this type of lamp has brought with it the Leed for more accurate aiming, but at the same time it has nabled aiming procedures to be simplified. Whereas with artier lamps an optical aimer was essential, because of ariations in the relative* positions of the filaments and the eflector, the fixed relationship of these items in the all-glass nit makes it possible to use a mechanical aimer working rom the outer face of the lens, three aiming " pads " being icorporated in the design of the lens for this purpose.

The all-glass, sealed-beam lamp is not running unopposed, owever. Even before its introduction on British vehicles. ystems embodying four headlamps, working in pairs, had stablished a foothold. As with many other aspects of the ritish automotive industry, commercial-vehicle man ufacirers were ahead of the private-car designers in the use of ten, the then Guy Motors, Ltd., and E.R.F., Ltd., together ith several passenger-body manufacturers, having made se of this equipment as far back as 1958.

With the four-headlamp system there is a pair of completentary lamps on each side of the vehicle. The lamps rming a pair can be either side by side, one above the her or positioned diagonally, the important thing being at there is one of each type on each side.

The lamps used in this system are metal-backed, sealedam units containing individually focused, soldered-in bulbs. It is not improbable that at some time in the near future all-glass, sealed lamps will be employed, the present types not being suitable for several reasons, one of which is that the paired lamps have a diameter of 51 in., compared with the 7 in. of the single units.

One of each pair of lamps contains double filaments: these give a 50W, dipped beam or a 371W. main beam. The other lamp has a single filament, which again gives a 374W. main beam with 12v. systems and 50W. with 24v. In the case of side-by-side layouts the single-filament lamps are positioned inboard of the twin-filament units.

In operation all four lamps are employed to produce the main beam, the combination totalling 150W. (or 175W. on 24v. vehicles), compared with the total of 120W. available from two all-glass, sealed-beam lamps. For the dipped beam the two single-filament lamps are extinguished, and the two 50W. filaments of the other lamps are employed, giving a total output of 100W.

The advantages of this system are obvious, and become even more so to anyone driving behind four such lamps. On main beam the range of illumination is even greater than that afforded by the all-glass, sealed lamps, whilst on dipped beam the higher wattage available enables a longer beam to be thrown along the near-side kerb without increasing the scatter of light to the off-side.

A later development, introduced at this year's London Motor Show, has been the "mixed," four-headlamp system which consists of two 7-in.-diameter, double-filament lamps paired with two 51-in.-diameter, single-filament units. This layout has been developed to give higher lighting efficiency when on the dipped beam because the 7-in. lamp gives better light-flux collection-22 per cent. greater than that of the 5i-in, unit—coupled with the fact that the 7-in, lamp can offer better control of the dipped beam. At the moment the normal, 7-in, unit is being used, but a true four-headlamp, 7-in, double-filament unit will be made.

Greater dipped-beam efficiency can be obtained despite the fact that the 7-in, lamp produces only a 45W. dipped beam, compared with the 50W. beam given by a 51-in. unit. However, in the near future the power of the dipped beam of the 7-in, lamp is to be raised to 50W., and the lighting efficiency of the unit should then be a clear 20 per cent. above that of the current 54-in. product.

There seems to be no earthly reason, therefore, for drivers to cling to their auxiliary lamps, once either of these two new headlamp systems become universal equipment, except when driving in fog or possibly falling snow. If the new installations can dissuade drivers from their perpetual use of dazzling pencil beams and the like, they and their fellow users of British roads should have due cause to be thankful for the efforts of British lighting engineers.

In any case, the increasing speeds of heavy vehicles are making the solo use of even the most powerful auxiliary lamps foolhardy: drivers will in time find themselves having to "Use their heads."

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