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5、rseding J2338 APR2010 Recommendations of the SAE Task Force on Headlamp Mounting Height RATIONALE The technical report covers technology, products, or processes which are mature and not likely to change in the foreseeable future. STABILIZED NOTICE This document has been declared “Stabilized“ by the
6、SAE Road Illumination Devices Standards Committee and will no longer be subjected to periodic reviews for currency. Users are responsible for verifying references and continued suitability of technical requirements. Newer technology may exist. Copyright SAE International Provided by IHS under licens
7、e with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2338 Stabilized FEB2011 Page 2 of 9 1. SCOPE The SAE International task force on headlamp mounting height has considered the ramifications of reducing the maximum mounting height of headlamps on highway
8、 vehicles. The task force has concluded that it is in the best interest of the driving public to make a substantial reduction in the recommended maximum height at which headlamps, particularly low-beam headlamps, may be mounted. Heights as low as 36 to 40 in (90 to 100 cm) have been considered. New
9、tractor vehicles are in fact being designed with headlamps mounted in this range. Further recommendations were withheld in anticipation of tests to demonstrate the effect of mounting height on the legibility of certain overhead signs. 1.1 Background For the past several years there has been increasi
10、ng concern on the part of automotive lighting committees within SAE and automotive lighting regulators at National Highway Traffic Safety Administration (NHTSA) over the glare from vehicle headlamps. Complaints to NHTSA from users indicate that both mirror glare and glare from opposing vehicles cont
11、ribute to the problem. Present mounting height standards allow headlamps to be mounted up to a height of 54 in (from the ground plane to the center of the headlamp). Generally, passenger vehicle occupants are seated such that their eye level ranges from about 40 in to 45 in. (100 to 114 cm). By comp
12、aring the range of vehicle drivers drivers eyes and mirrors with the range of headlamp heights, it can be shown that passenger vehicle drivers eyes and the vehicles rearview mirrors can be located below the top cutoff of the projected beam of a following vehicle. In this high gradient zone, the ligh
13、t intensity from a lower beam headlamp beam, located 40 ft behind a drivers rearview mirror, will increase at least 20% (40% in some lamps) for every 1/10 degree (0.84 in) below the top cutoff of the beam pattern. For a rearview mirror located 5 in below the top cutoff of a headlamp beam pattern, th
14、e beam gradients of 20 to 30% per 1/10 degree would cause an increase of 300% to 500% of the light that a driver would experience if the mirror were located exactly at the top cutoff. A 1000% increase in eye illumination could be experienced in comparison to that from a mirror located at an approxim
15、ately equal distance above the top cutoff. These numbers give us a clue as to why passenger vehicle drivers are noticing the differences in glare from high-mounted headlamps. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted witho
16、ut license from IHS-,-,-SAE J2338 Stabilized FEB2011 Page 3 of 9 1.2 History The conflict between where passenger car drivers are located and where vehicle headlamps can be mounted can be traced by reviewing historical trends in vehicle lighting. Passenger vehicle sizes and heights are decreasing as
17、 many vehicles are being downsized and as a result, the elevation of drivers eyes and rearview mirrors has been reduced accordingly. Light trucks (pickups, vans, minivans and sport utility vehicles) on the other hand, are not decreasing in either size or market share. With headlamps routinely mounte
18、d well above those on passenger cars, light trucks are more popular than ever. The higher mounting heights on these vehicles most likely represent a substantial part of the increase in complaints about headlamp glare. When headlamp mounting height standards were first written, headlamps on passenger
19、 vehicles were routinely mounted at 30 or even 32 in (approximately 79 cm) above the ground plane, 8 to 10 in above the 22 to 24 in (approximately 58 cm) mounting height we see today. It is probably safe to assume that the eyepoint of the driver was also higher by 8 to 10 in. If we use 44 in (112 cm
20、) for todays passenger car driver, a rearview mirror mounted 2 or 3 in (6.4 cm) above the drivers eye in the old standard-setting vehicles would have an elevation of 54 to 57 in (44 + 8 + 2 to 44 + 10 + 3 in), approximately 141 cm. This is essentially identical with the maximum mounting height of th
21、e headlamp that was prescribed at that time. Another reason for the recent trend of dissatisfaction and irritation with vehicle lighting among passenger vehicle drivers may be found in the headlamp beam intensity distribution itself. In one of the first SAE photometric standards, J579a, the required
22、 light level was only about 75% of the present standard and only 60% of more advanced standards in Federal Code 49 CFR Part 571.108. In fact, contemporary halogen headlamps generally achieve 100% more light at the 1/2-degree-down seeing point than was available from the brightest of the SAE J579a de
23、sign headlamps. At the time the mounting height standard was defined, a driver would have been exposed to roughly about 2800 cd viewing a following vehicles 54 in mounting height headlamps (designed to SAE J579a) in his rearview mirror. Today rearview mirrors (front surface, prism) in their “night“
24、position may reflect as little as 4% of the incident light. In spite of their elevation in the headlamp beam, the glare concern for rearview mirrors is low compared to drivers side view mirrors. A side view mirror (no “night“ adjustment; 50% reflectance), mounted at about 40 in or less, could theore
25、tically be over 1.6 degrees below the horizontal of a headlamp mounted at 54 in / 137 cm. At a distance of 40 ft (12.2 m) on some halogen headlamps using axial-filament light sources, this is the approximate location of the maximum beam intensity (MBI). MBIs of over 30 000 cd are possible. This repr
26、esents more than a tenfold increase of the exposure intensity over that which was typical when the standard was formulated. It is apparent that mounting height or aiming guidelines must be revised to accommodate the changes in aerodynamic vehicle styling and headlighting technology. The most technic
27、ally defensible solution is to lower the current maximum mounting height for headlamps in order to reduce the maximum exposure level to a reasonable value. 2. REFERENCES 2.1 Applicable Publications The following publications form a part of this specification to the extent specified herein. 2.1.1 Siv
28、ak, M., Flannagan, M., Gellatly, A.W., “Influence of Truck Driver Eye Position on Effectiveness of Retroreflective Traffic Signs,” Ltg. Res. Technology, 25(1) 31-36, (1993) 2.1.2 Cobb, J., “Roadside Survey of Vehicle Lighting 1989,” Transport and Road Research Laboratory, U.K., Research Report 290,
29、(1989) 2.1.3 Kosmatka, W.J., “Obstacle Detection with Headlamps: Threshold Luminance or Contrast,” Proceedings of IES, IENSA Conference - 1995, (1995) 2.1.4 Kosmatka, W.J., “Obstacle Detection Rationale for Vehicle Headlamps,” J of the IES, Winter 1995, 36-40, (1994) Copyright SAE International Prov
30、ided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE J2338 Stabilized FEB2011 Page 4 of 9 3. REVELANT ISSUES IN LOWERING RECOMMENDED HEADLAMP MOUNTING HEIGHTS It is certain that the greatest effect of such recommendations would be f
31、elt in the truck, tractor-trailer and pickup vehicle manufacturing industries. Passenger vehicles, with few exceptions, already have their headlamps mounted in the range of 22 to 26 in (56 to 66 cm). The body contours and bumper location preclude higher mounting in most passenger vehicles; vans are
32、the notable exception. With this background one can understand why most of the following discussion centers on truck types of vehicles. Two issues are frequently raised on the subject of lowering the mounting height of headlamps: a. The resulting increase in the vertical separation between the drive
33、rs eyepoint and the headlamp light source on large trucks will decrease the conspicuity and legibility of retroreflective traffic control devices and highway information signs which are illuminated solely by the vehicle headlamps. b. There will be a reduction in the visibility distance of the operat
34、or and this will reduce the chances of stopping the tractor-trailer or truck vehicle within the obstacle detection distance. 4. UNLIT TRAFFIC CONTROL DEVICES Luminance of retroreflective overhead highway information signs (which are illuminated only by vehicle headlamps) will be reduced by virtue of
35、 the increased observation angle. The observation angle is the angle formed by a line between the drivers eye and the sign, and another line between the light source and the sign. As the drivers eye position moves upward, away from the headlamp, or as the headlamp height is lowered, the observation
36、angle increases. For retroreflective materials, the level of light returned to an observer is reduced as the observation angle is increased. The implications of separation distances are discussed by Sivak, Flannagan and Gellatly (see 2.1.1). Without a doubt, a loss of legibility of the sign informat
37、ion is undesirable. But this reasoning may be overly simplistic in the assumptions that it makes. It implies that a driver cannot take measures to compensate for the loss of visual information. Moreover, the argument ignores precedent. Some vehicles being driven on highways today already have extrem
38、e observation angles with no documented ill effects. In order for the driver to suffer the loss of sign legibility as the direct result of headlamp location, the headlamps on his own vehicle must be the only source of illumination on the sign. On heavily traveled highways where lower beams are gener
39、ally required, sign illumination is frequently the result of illumination by multiple sources, each having its own particular intensity and observation angle for the drivers in the immediate vicinity. A loss of 20 or 30% of sign luminance from one vehicle may not even be noticeable, let alone consti
40、tute a safety issue under these conditions. In low traffic situations, a single vehicles headlamps are sometimes the only source of sign illumination. If the operator needs the sign only as a reminder of a predetermined route or direction, then it is difficult to argue the safety implications of red
41、uced sign legibility. Assuming that the vehicle operator really does need the information presented to make a decision, the driver is still able to exert control over the time available to view a sign. In this situation vehicle operators are able, at their option, to control the time available to fo
42、rmulate a decision by a reduction in the vehicles speed. If the roadway traffic is light as postulated, then a reduction in speed, a lane change, or a momentary switch to high beam are all possible. A comparison of truck headlamp mounting heights and vertical separation of the drivers eyes from the
43、headlamps is depicted in Figure 1. This is a compilation of recent data provided by truck and tractor vehicle manufacturers. The parameter of the drivers eye height is noted also. The chart makes several important points: Copyright SAE International Provided by IHS under license with SAENot for Resa
44、leNo reproduction or networking permitted without license from IHS-,-,-SAE J2338 Stabilized FEB2011 Page 5 of 9 FIGURE 1 - HEADLAMP AND DRIVER EYEPOINT ELEVATION - HEAVY TRUCK MGR. SURVEY: 1993 a. The average (or median) mounting height of a headlamp is about 45 in (114 cm). b. There are situations
45、where a relatively great separation between the drivers eyes and the light source (e.g., the observation angle) already exists. There are several instances in which the location of the drivers eyepoint is above the headlamp by 60 to 70 in (152 to 178 cm). c. There are trucks on the road with headlam
46、ps mounted at 40 in (102 cm) or lower. A study of vehicle lighting (see 2.1.2) also shows that there are many European trucks with headlamps mounted at 90 cm (36 in) and below. Interpolation of Cobbs data would indicate that the vast majority of articulated vehicles measured had headlamps mounted be
47、low the 90 cm height. Based on these data, and having no information that the vehicles noted above have caused drivers to experience problems with large observation angles, the argument that a loss of sign legibility will have dramatic negative safety effects does not appear to be substantiated. Dri
48、vers viewing oncoming traffic from elevated positions actually experience a substantial reduction in glare and therefore their eyes remain more consistently dark-adapted. 5. DETECTION DISTANCE EFFECT The detection or discernibility distance for headlighting systems has been studied in real roadway s
49、ituations and with mathematical algorithms over the years. In almost all cases these studies concentrated on passenger vehicles. In most of these cases mounting height was not the issue. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted witho
