More Light on the Headlighting Problem

Transcription

1 More Light on the Headlighting Problem VAL J. ROPER and G. E. MEESE Miniatre Lamp Department, General Electric Co., Nela Park, Cleveland, Ohio S there any practical ay that seeing can be improved ith the loer beam? Can the annoyance of headlamp glare be redced? What is the effect of the headlamp monting height on today's cars? Ho abot the ne qart iodine headlamps that are being promoted in Erope? Ho mch does alcoholin the driveraffect seeing distances? Ansers to these qestions ere soght in a recent series of seeingdistance tests sing opposing cars ith observerdrivers and observerpassengers. The procedre as similar to that described in "Seeing Against Headlamp Glare." (1) To opposing cars, radio eqipped and ith the test headlamps, e re started some 4, ft apart on a 2lane highay, accelerated niformly to 4 mph ith this speed maintained throghot the test rn. Test obstacles 16 in. sqare and ith 7 percent reflectance (dark gray) ere placed at the right edge of the traveled roaday. There ere a total of 1 obstacles, 5 ahead and 5 behind the meeting point. The observerdriver and observerpassenger ignored the obstacles on the left side of the road. They atched for the obstacles on the right side of the road only and indicated the moment of detection by pshing a btton. The btton actated a pen hich marked a tape recorder geared to the transmission. A sfficient nmber of repeat rns ere made to get a fair average of the seeing distance vales as the to cars approached, passed at the meeting point and proceeded beyond. The data ere plotted in crves ith the seeing distances as ordinates and the distance beteen cars as abcissae p to the point of meeting, and the distance behind the meeting point after the point of meeting. Referring to the qestion on loer beams of sealed beam headlamps, present loer beams are no manfactred to meet specifications established by the Society of Atomotive Engineers. These specifications are intended to cover a beam pattern hich represents the best compromise beteen the reqirements of seeing and glare relief. Minimm candlepoer vales are prescribed for those parts of the beam hich are important from the standpoint of seeing ahead, and maximm candlepoer vales are provided for those parts of the beam hich are apt to be directed at the opposing driver's eyes. A very important seeing distance point in the l oe r beam is the socalled 1/2 don, 2 right point, hich is 1/a belo the level of the headlatnp centers and 2 to the right of straight ahead of each headlamp. Present SAE specifications call for a minimm of 6, candlepoer at this point from each headlamp and a maximm of 1, candlepoer at this point from each headlamp. Figre 1 shos the average seeing distance vales on a straight level roaday obtained in these tests for 6,, 1, and 2, candlepoer (loer beam) at thi s % don, 2 right point hen approaching, meeting and proceeding beyond an opposing car ith exactly the same beam candlepoer vales. Lamps ere properly aimed and at 31in. monti ng height. A consider able gain in seeing distances is obtained ith the beam providing 2, candlepoer at the point 1/2 don, 2 right. n reference to the alleviation of headlamp glare, anyone ho has the opportnity to take part in tests of this kind soon learns that if the driver hen meeting other vehicles at night ill alays direct his attention along the right edge of the lane of travel (and particlarly avoid looking at the opposing headlamps) the annoyance of glare is greatly redced and the seeing distances considerably increased. Under this condition, one need not focs the attention exactly straight ahead, nor to the left side of the road. Paper sponsored by Special Committee on Night Visibility and presented at the 43rd Annal Meeting. 29

2 1 <{ 1 3 <) 2 <) 1 2. Cp,...:._ NO ATTENTON FACTOR APPLED,,,,.... / r / &. 1, c p_ l,.../ C> STRAGHT, TWO LANE ROAD l. 4UO BOO 4 4 BOO 12 1 DSTANCE BETWEEN APPROACHNG CARS DSTANCE BEYOND FEET MEETNG PONT Figre 1. Average seeing distances. NO ATTENTON FACTOR APPLED <{ 1 3 <) 2 Ld <) 1 l CURVE OUTSDE LANE 2. Cl' 1, ce s.o o t:: r=:;:... /, DSTANCE BETWEEN APPROACHNG CARS DSTANCE BEYOND MEETNG PONT Figre 2. Seeing distances (12,ft crve radis). NO ATTENTON FACTOR APPLED <{ 1 3 <) 2 <) 1 2,o CF!, /' 1,,...v 1. c 1... r_ / v / c:,,,, 11 r CURVENSDE LANE l DSTANCE BETWEEN APPROACHNG CARS DSTANCE BEYOND MEETNG PONT Figre 3. Seeing distances (12,ft crve radis).

3 Peripheral vision is sfficient to detect anything hich crosses the road from left to right beteen the to cars. Fortnately, silhoette seeing (2) also serves to disclose sch obstacles. Althogh greater seeing distances old reslt from increasing the candlepoer at the specified point to 2, on a straight road, hat is the effect hen negotiating a crve against oncoming traffic? To anser this qestion, tests ere repeated in a similar manner, bt hile negotiating a crve having a radis of 12, ft. Dring the period of approaching the other vehicle, one of the to cars had its headlamps pointed almost directly toard the opposing vehicle, and the other of the to cars had its headlamps pointed aay from the opposing vehicle (Figs. 2 and 3). Figre 2 covers the sitation of the driver and observer having the opposing headlamps pointed directly at them; Figre 3 covers the sitation herein the opposing headlamps are pointed aay from the driver and observer. Again, the observers ere prposely directing their attention along the right side of the traveled lane, and definitely avoided staring at the opposing lamps. f drivers can be edcated to do this, a loer beam providing higher candlepoer vales near the center of the road or the center of the traveled lane can definitely provide added safety in terms of seeing distances verss stopping distances. n these tests, the opposing vehicles ere in adjacent lanes, ith no separation beteen lanes other than a hite line. On trnpikes or freeays here there is separation beteen the opposing lanes, the effect of glare is redced, the more the separation beteen lanes, the greater the redction in glare. Therefore on freeay or trnpike driving, the seeing distance capability can be expected to be considerably greater than the vales shon in Figres 1, 2, and 3 (1). n the previos cases, the headlamps on both test cars ere properly aimed. Misaim of the loer beam either redces the seeing distance or increases glare to the approaching drivers. f the candlepoer is increased near the top of the loer beam and near the center of the road, there is of corse a likelihood of increased glare if the lamps are misaimed high, and/or to the left. To determine the effect of misaim ith candlepoer at the 1 /2 don and 2 right point, another series of tests as rn ith 2, candlepoer from the headlamps on one car and 8, candlepoer from the headlamps on the other car. The latter candlepoer as selected becase it is miday beteen the minimm and maximm candlepoer specified by the SAE for this point. Figre 4 shos the reslts of 2, candlepoer misaimed p and to the left facing 8, aimed correctly and 8, candlepoer facing 2, (misaimed) compared ith 8, candle 31 NO ATTENTON FACTOR APPLED f 5 c:, 4 <( f 3 VJ oo VJ 1 Z. CP. (MSAM D FACNG i.coo CP >TCJLr!L,.oo o Cf'..;..:..._ / :::/ B.OOO CR i'acnc ZC CR!'!SAMEC)) i DSTANCE BETWEEN APPROACHNG CARS DSTANCE BEYOND MEETNG PONT Figre 4. Seeing distances on a straight 2lane road (for reference the dashed crve shos to cars sing prodction lamps properly aimed).

4 32 poer facing 8,. f the loer beam candlepoer is increased, the drivers of old cars ill sffer some loss in seeing distance hen facing ne cars if the ne car headlamps a r e misaimed high and to the left, bt pr actically no loss in seeing distance if the ne headlamps are correctly aimed. The effect of headlamp monting height on seeing distance, in the case of the pper beam hich provides high beam candlepoer vales at the level of the headlamp centers and above, is negligible. Shold the pper beam headlamps be monted mch loer than at present (for example, 12 or 18 inches above the grond) shados old be cast by rogh spots in the road hich co11ld be annoying; hoever, this is not a serios factor at the present minimm monting height of 24 inches from the grond to the center of the lamps. n the interest of a lo silhoette hich seems to have poplar pblic approval, the headlamps have been loered from an average of 3 to 32 inches several years ago to 24 or 25 inches from grond to center of lamps at present. This definitely redces the seeing distances available ith the loer beam becase the high candlepoer vales in the loer beam mst be directed belo the level of the headlamp centers. f 5 <( f 3 (/) 2 (/) 1 NO ATTENTON FACTOR APPLED.. E G J1T 3 1 MOUNTNC,,,. 26" MOUNTNG HEG r..._ / 'L.. Z4 ooo 1 12! 4 4 BOO 12 1 DSTANCE BETWEEN APPROACHNG CARS DSTANCE BEYOND FEET MEETNG PONT Figre 5. Effect of lamp monting height. NO ATTENTON FACTOR APPLED f 5 <( f 3 (/) 2 (/) 1 _... _s.ooo CF' r S) r:...;...::."'...:.'"' QUARTZ ODNE (EUROPEAN)..._ BOO 4 4 BOO 12 1 DSTANCE BETWEEN APPROACHNG CARS DSTANCE BEYOND FEET MEETNG PONT Figre 6. Comparison of prodction American and Eropean (Ferra E) loer beams ith 62 Qartiodine blbs.

5 Theoretically, the geometry of the sitation indicates that, considering the important seeing distance point 1 /2 don and 2 right, 1 feet in seeing distance shold be lost for every inch the headlamp height is loered. Therefore, hen the headlamp height is loered from the 31 inches of several years ago to 25 inches no, 6 feet in seeing distance is lost. As a check, the test of the 1, candlepoer crve (Fig. 1) as repeated bt ith the headlamps monted at 26 inches above the grond instead of the 31in. monting height. Figre 5 shos that the average seeing distance loss checks very ell ith the theoretical calclation. Althogh the stylists and the pblic old probably not accept car designs that old place the tops of the headlamps above the fender or hood line, it shold be feasible to raise them a fe inches above the present 24in. minimm vale (grond to headlamp centers) ith a sbstantial gain in seeing distances. n this contry, the maximm beam candlepoer alloed from the pper beam of headlamps is 75,. The Uniform Vehicle Code and the las of the states do not in 33 NO ATTENTON FACTOR APPLED f soo _ 4 f 3 VJ 2 VJ 1 CURVE OUTSDE LANE.No l. A,._ " ALco_ Lco11L.,.._ DSTANCE BETWEEN APPROACHNG CARS DSTANCE B E YOND " FEET.. MEETNG PONT Figre 7. Effect of to "short" drinks on seeing distance. NO ATTENTON FACTOR APPLED f 5 _ 4 f 3 VJ oo VJ 1 CURVENSDE LANE.... AL CO MO 1yOt... _..,./ / DSTANCE BETWEEN APPROACHNG CARS Figre DSTANCE BEYOND MEETNG PONT Effect Of to "short" drinks on seeing distance.

6 34 elde this vale. Hoever, it is part of the SAE specifications hich most states se as a criterion to determine hether the headlamps jstify their approval. The Eropean and international maximm is 3, beam candlepoer. American engineers and lighting experts feel that any vales mch above the present SAE maximm of 75, old make it virtally impossible to se an pper beam, in vie of traffic conditions in the United States. Hoever, for many areas in Erope otside of tons, there is very little traffic, hence their pper beam of considerably higher candlepoer gives ver y pleasing reslts. The Eropean loer beam (not inclding the English loer beam) featres a very sharp edge at the top. The filament in the sal parabolic reflector is placed considerably ahead of the focal point, ith a shield nderneath hich shados the entire loer half of the reflector. This in effect thros aay half of the possible light otpt in the beam, bt it provides above horiontal candlepoer vales hich are a fraction of ors. Comparative tests of the type described in this paper have shon that the typical Eropean lo.. e r beam provides less seeing distance along the right side of the road, bt more seeing distance along the left side of the road. The reason has been that or sealed beam loer beams have provided more candlepoer near the top of the beam on the righthand side, bt the depression on the lefthand side has been an average of abot a degree more than that in the case of the Eropean loer beam. One of the major advantages of the sealed beam headlamp is the elimination of the effect of "blb blackening." n the case of the qart iodine lamp, there is very little blb blackening. nstead of depositing on the blb srface, the evaporated tngsten redeposits pon the filament. This permits the se of a tngsten filament of higher efficiency and therefore higher brightness. Throgh the cortesy of Carello of Trin, taly, to pairs of Eropean headlamps sing qart iodine blbs ere obtained. These headlamps provided a loer beam only. They ere part of a 4lamp system, the pper beam provided by a separate pair of lamps. Figre 6 shos the comparison of reslts on the straight level 2lane road o the Carello loer beam poered by a 62 qart iodine blb and a typical average sealedbeam loer beam of 8, candlepoer at the specified point. The athors feel that the Eropean design does not take fll advantage of the possibilities ith the qart iodine lamps. nasmch as the test road (an as yet nsed section of a ne freeay) had no traffic other than or on, e decided to measre the effect of "to drinks" after dinner. Therefore, immediately after the test covered by the 1, candlepoer crves of Figres 2 and 3, in the corse of abot onehalf hor, the drivers and observers had to drinks totaling a little less than thr ee 86 pr oof onces and r epeated the t est. The reslts are shon in Figres 7 and 8. ncidentally, none of the participants felt that they ere at all nder the inflence of alcohol, yet their seeing distance as redced. REFERENCES 1. Seeing Against Headlamp Glare. llminating Engineering, Vol. 47, No. 3, March Silhoette Seeing ith Motor Car Headlamps. Trans. E S, 1939.