Under I'mierent Headlamp Low-Beam

358 J. Light & Vis. Env. Vol.32, N0,4, 2008

Rese~rch No'te A Study on Peripherai Visibility under ~i'Mierent Headlamp Low-beam Pattern

Wencheng CHEN*, Yandan LIN', Shinichi KOJIMA- and Dahua CHEN*

~stituteforElectriclightScu~~FudanUhive~ty, Shanghai200433, China fydliE@fudarLed~c~) ~~seai~h & Devekyznent Cen:te~; Starley Ekxtric Ce., L~d, Japan

Received December 25, 2007, Accepted June 10, 2008

ABSTRACT In this article peripheral visibility under the condition of three types of head]amps' Iow-beam pattern was com- pared with the Two-Alternative Forced-Choice (2AFC) method. The three headlamps used in this night-time ~e]d stvdy were headlamp No. 1: Parabolic-HID, Headlarnp N0.2i Projector-HID 8nd Headlarnp N0.3: Para- bolic-Halogen. The results show that HID headlamps are better for the detection of pedestrian in periphera] than halogen headlamps because of the higher light output, higher color temperatvre, brighter foreground and wider spread of light. Some suggestion abovt criteria of the automobi]e head]ight distribvtion for Chinese traffic condition was also discussed.

KEYVVORDS: automotve lightng, Iow-beam pattern, perlpheral visibility, nighttime driving

1. Introduction efficacy (lumens per watt) and longer lifetime. With the Headlights are required equipment for all cars. The benefit of small source size of HID headlamps, some function of vehicle mounted headlamps was to illumi- new reflector design technology, for example the projec- nate the street and surrounding area during night time tor type of headlamp, was developed. A projector head- drivingl). The effectiveness of a variety of driver visual light produces a stronger beam compared to most para- aids depends on the mumination from headlamps. For bolic headlights and muminates a more focused area, example, retroreflective trafflc signs and lane markings providing fewer of what we called "scatter loss"4) are visible primarily because of the reflected headlamp As a preparation of this research, an investigation on illumination2). The innovation in front lighting has been traffic condition and driver's behavior in China was concentrated on improving light output and optimizing done through questionnaires on 90 subjects. The results light distribution. The front lighting systems must meet showed that the urban road was more crowded and specific requirements standardized in terms of their wide spread low beam pattern was preferred by drivers distributions of luminous intensity and color3). for detecting other road users around the vehicles, such The distributions of luminous intensity are specified as pedestrians and cyclists. In the field study we com- so that headlamps will illuminate the areas of the pared the visual performance of drivers under three roadway important to a driver without causing exces- different types of headlamps' Iow beam without road sive glare to oncoming drivers or to passers-by along the lighting and opposing glare lights. The three headlamps roadway. The photometric standard of automobile light- used in this nighttime field study were Headlamp No.1: ing in China is based on European system, which sug~ Parabolic-HID, Headlamp No.2: Projector-HID and gests a narrow beam pattern and a sharper cutoff, as Headlamp No.3: Parabolic-Halogen. The field experi- shown in Figure I . ment was designed according to 2AFC method5). The With the development of lighting technology, many percent of correct (pc) in this 2AFC detection experi- new headlamps came into the market in recent years: ment was recorded and then the value of discriminabil- the halogen tungsten lamps, the high pressure gas dis- ity index (d~ was calculated as the criteria to evaluate charge lamps, first called Xenon and at present known the visibility of the pedestrian under each headlamp . as the High Intensity Discharge (HID) Iamps. Moreover, nowadays manufacturers already equip their concept 2. Metho(ls cars with LED headlamp. 2.1 Subjeets HID headlamps have several advantages over tung- Nine subjects, three females and six males, aged from sten halogen headlamps, including greater luminous 20 to 25, participated in all the experiments. The sub-

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362 J. Light & Vis. Env. Vol.32, No.4, 2008

Table 2 The mean values and the standard deviation of percent oorrect for three headl8mps at five positions

Percent correct (o/o) Headlamp 3 Headlamp l Headlamp 2 Distance(m) (Parabolic type, (Parabolic type, HID) (Projector type, HID) Ha]o*'en) Mean SD Mean SD Mean SD 30 91 10.5 96 7.3 90 12.3 35 92 8.3 93 7. 1 89 l 9.7 40 89 S O.5 92 9.7 86 l Z .3 45 82 10.9 86 18.{ 81 1 6.2 50 89 9.3 82 l 5.6 74 13.3

Teble 3 llluminanoe values measured on a vertical surfa~ (1 m and 0.1 m above the ground) at five positions for three he8dlam ps

Vertical iliuminance (1x)

Distance(m) Headlamp l Headiamp 2 HeadkuTlp3 (Parabohc type, HID) (projector type, HID) (Paraboiic type, Haiogen~

l lergh~ I m 1-Ieight=0. I m Ileight ~m lieight=0,~m Heigh~ I m I Ieight=0. I m

30 6.9 5.3 6,4 1 5.7 1 .9 2.4 35 5,7 5.3 5,4 13.1 2.2 2.4 40 4,8 4.9 5,0 lO.8 2. l 2.3

45 4.5 4.6 4.6 8.9 2. 1 2.2 50 4*~~ 4. 1 4.0 7.4 2.3 2.0

~- Xe~d]~mpl (p~r~~0lic type, HiD) ~oO ~~ Headl~mp2 (projector type, HID) 12 -4Headlarn 3 a~abo[iet e, H~ O en ~ -,- H*,d]*~P2 95 iO -*- H**di,~ 3 ~ 90 >< ~~ ~: 8 ¥,¥¥'¥¥' R (, c:v (D (Q ~: 85 ~: 6 8 E ~¥¥_:~~ :, E;e, ~~~, o as ,*.-*~~~. e) 80 ~L ~:o 4 >e) 75 2 A A * ' * 70 C 35 30 40Dist~ nce45 Im 50 3a 35 Dista"~40 l* 45 50 Flgvre 8 Percent oorrect ploWed at distan~forthree headlamps Figure 9 Vertical illumianoe plotied at distanoe for three head]am ps percent correct for three headlamps at ~ive positions m except at 50m for headlamp 1. At distance of 30m to were shown in Table 2. The vertical illuminances were 45 m, percent correct under the condition of headlamp 2 measured at the height of I m and 0.1 m from the is the best. At distance of 50 m, percent correct with ground at five positions under three headlamps and the headlamp I is the best. Percent correct with headlamp values were shown in Table 3. 3 is the lowest for all distance among the three head- Figure 8 shows the results of percent correct as a lamps. Figure 9 shows the results of the average verti- function of distance for three headlamps. Percent cor- cal illulninance at five distances for three headlamps. rect decreased with increasing distance from 30 m to 50 In order to get more inf;ormation from the reslalts,

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J. Light & Vis. Env. Vol.32, N0.4, 2008 365

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