Single Headlamp with Low- and High-Beam Light

hv photonics

Article Single Headlamp with Low- and High-Beam Light

Shang-Ping Ying 1, Bing-Mau Chen 1,*, Han-Kuei Fu 2 and Chen-Yu Yeh 1

1 Department of Electro-Optical Engineering, Minghsin University of Science & Technology, Hsinchu 30401, Taiwan; [email protected] (S.-P.Y.); [email protected] (C.-Y.Y.) 2 Electronic and Optoelectronic System Research Laboratories, Industrial Technology Research Institute, Hsinchu 31040, Taiwan; [email protected] * Correspondence: [email protected]

Abstract: Generally, automobiles are typically equipped with separate headlamp lanterns for generating low- and high-beam light. Compared with separate headlamp lanterns, a single headlamp producing both low- and high-beam light can be more compact and have less mechanical complexity. The single headlamp structure has become a main emphasis of research that manufacturers will continue to focus great efforts on in the future. A novel design of a single headlamp generating both low- and high-beam light is proposed in this study. The proposed headlamp consists of a compound ellipsoidal reflector, a baffle plate, a condenser lens, and LED array devices generating low- and high-beam light. The compound ellipsoidal reflector comprises a primary ellipsoidal reflector for generating low-beam light and a secondary ellipsoidal reflector for generating high-beam light. Monte Carlo ray tracing simulations were performed to confirm the optical characteristics of the proposed design. A prototype of the proposed headlamp was also fabricated and assembled to verify the design’s effectiveness. The simulated and measured illuminance distributions of the low-beam and high-beam light had the desired light patterns. Moreover, all the simulated and measured illuminances of each point and line met the ECE R112 regulation for low-beam and high-beam light. The proposed headlamp in this study is feasible for the application of single headlamp generating

both low- and high-beam light.

Citation: Ying, S.-P.; Chen, B.-M.; Fu, Keywords: optical design and simulation; light-emitting diode; vehicle lighting H.-K.; Yeh, C.-Y. Single Headlamp with Low- and High-Beam Light. Photonics 2021, 8, 32. https:// doi.org/10.3390/photonics8020032 1. Introduction In the initial stage of development of the automobile industry, headlamps were Received: 23 December 2020 primarily used to illuminate roads, and no requirement existed pertaining to long-range Accepted: 25 January 2021 illumination or light beam shape. However, with the rapid development of light sources, Published: 27 January 2021 automotive lighting technology and high-efﬁciency light sources have become highly integrated. Currently, the major objective of vehicle lighting is to improve the driver’s Publisher’s Note: MDPI stays neutral visual performance at night or in dark places. In the last two decades, incandescent and with regard to jurisdictional claims in tungsten halogen bulbs have been used in vehicle lighting, and presently, high-intensity published maps and institutional afﬁl- discharge (HID) bulbs are implanted into some products. Light-emitting diode (LED) iations. lighting exhibits some favorable characteristics, such as long life, high reliability, resistance to vibrations and shocks, high environment friendliness, low power consumption, small size, and high feasibility for the optical design of light beam shape. Their continued improvement makes it realistic to project LEDs as a promising technology for vehicle Copyright: © 2021 by the authors. lighting [1–3]. For vehicle lighting, a well-designed headlamp can enable drivers to guide Licensee MDPI, Basel, Switzerland. the vehicle safely at night along roads of varying geometries and to identify pedestrians This article is an open access article and obstacles. For designing the light beam shape, various beam-shaping strategies for distributed under the terms and LED lighting [4] and LED-based automotive headlamps [3] have been proposed. conditions of the Creative Commons Automobiles are generally equipped with separate headlamps for generating high- Attribution (CC BY) license (https:// and low-beam light. High-beam light offers superior visibility when driving at night on a creativecommons.org/licenses/by/ 4.0/). deserted stretch of road. However, this light is too bright and can cause night blindness

Photonics 2021, 8, 32. https://doi.org/10.3390/photonics8020032 https://www.mdpi.com/journal/photonics Photonics 2021, 8, 32 2 of 13

in oncoming drivers. In this case, a low-beam light directed toward the road without blinding the drivers in the front should be used. The Economic Commission for Europe (ECE) R112 regulation has declared clear low- and high-beam lighting requirements as well as measurement methods for lighting areas and spill zone intensity [5]. According to the regulation, high-beam light should only be used to illuminate far-off distances where visibility is mostly low in the absence of streetlights, thereby enabling long-range illumination of the road surface. The shape requirements for low-beam light can prevent the glare impact caused on a driver by a car moving in the opposite direction; thus, accidents can be prevented. According to brightness of the illuminating area affecting the traffic information when driving, it must meet the regulations of spill zone intensity to illuminate the billboard road information. Therefore, the optical design of low-beam light is the most difficult aspect in automotive lighting. To achieve regulation requirements, three basic structures have been proposed for traditional low-beam headlamps that use tungsten halogen or HID sources: reflector optics, projector module, and lens optics. To meet the ECE R112 regulation, all headlamps should provide a low-beam cutoff line. However, the optical characteristics of white LEDs are highly different from those of tungsten halogen or HID sources. Moreover, the output power generated from a single LED is less than that generated by exiting light sources. Thus, multiple LEDs are required for designing an LED headlamp. The expected optical design of an LED headlamp that can obtain a regulated light pattern with high efficiency depends on the optical characteristics of the LEDs forming the headlamp. Several complicated LED headlamp lenses have been developed [6], such as a lens that can transform the emergent ray into a rectangular beam region [7]; a low-beam LED headlamp based on microlenses [8]; an automotive headlight system incorporating digital micromirror devices [9]; an optical system with an ellipsoidal reflector, a baffle, and a faceted reflector [10]; an LED design with four main components: a focal LED, asymmetric metallic plate, freeform surface, and condenser lens [11]; a low-beam headlamp designed with Oliker’s ellipses technology [12]. Projector-type headlamps are substantially brighter in a focal spot than reflector headlamps are and, thus, can provide maximum vision when driving at night. Moreover, projector-type headlamps are less likely to cause night blindness in oncoming drivers because they are directed toward the road rather than the eyes of the drivers. Depending on their design and commercial use, projector-type LED headlamps can offer considerable benefits in vehicle lighting. Automobiles are typically equipped with separate headlamp lanterns for generating low- and high-beam light. These lanterns are mounted adjacent to each other in the front of the car. Compared with conventional separate headlamp lanterns, a single headlamp producing both low- and high-beam light can be more compact and have less mechanical complexity. Moreover, the reduction in the number of parts and degrees of freedom during a single headlamp’s assembly simplifies the alignment of different light functions relative to each other. To produce both low- and high-beam light by using a single headlamp with halogen or HID bulbs, a movable shield or light baffle has been integrated into a projector- type headlamp [13,14]. For low-beam light, the shield blocks a portion of the lamp output to achieve the desired cutoff line. For high-beam light, the shield is moved out of the way and the light is allowed to pass through to enable long-range illumination of the road surface. However, because the moving parts in the structure are controlled by an electromagnetic actuator or a piezotranslator, which gradually deteriorates with time and changes in the environment and temperature, they can cause device failure. The aforementioned problem is a serious issue in vehicle lighting. To address this issue, white LEDs can be used to develop a single headlamp generating both low- and high-beam light. Zhu used an LED array to develop a single headlamp generating both low- and high-beam light [7], where a second optical lens was used to concentrate the light generated from the LED array to form a beam region on the screen. Then, different blocks were illuminated by lighting up different LEDs in the LED array to realize low- and high-beam lighting simultaneously. However, the uniformity of multiple LEDs in a single lifespan and the complicated circuit configuration were the challenges faced in this design. A compact LED composed of two Photonics 2021, 8, 32 3 of 13

rows of LED chips was also used as an automotive headlamp light source combining low- and high-beam light [2]. The primary optics in the structure collected the emission of the two closely spaced chip rows and simultaneously separated the respective contributions. Then, the secondary optics, which were based on a faceted reflector, were used to shape and realize the low- and high-beam patterns. The structure of a projector-type LED headlamp can be used to obtain both low- and high-beam light from a single headlamp. The light emitted from the low-beam LED array is reflected by the ellipsoidal reflector and cut off by the vertically oriented light baffle. Then, a low-beam output with a bright or dark edge is transmitted through the lens to form the desired cutoff line. Moreover, the lower surface of the vertically oriented light baffle is designed to redirect the light emitted from the high-beam LED array through the lens. The additive light reflected from the lower surface of the vertically oriented light baffle is transmitted through the lens and forms a bright or dark edge lacking high-beam light [15]. In a previous study, a single headlamp producing both low- and high-beam light was achieved with the reflected light baffle in a projector-type headlamp by adopting a condenser lens with a specific second surface to spread the light and obtain a predetermined beam pattern [16]. However, the structure of this condenser lens is complex, and difficulties exist in its manufacturing process. To address the aforementioned issues, the present paper proposes a novel LED headlamp design with a projector-type structure, in which both low- and high-beam light are generated using a single headlamp. As shown in Figure1, the compound ellipsoidal reflector comprises a primary ellipsoidal reflector with a low-beam LED array device for generating low-beam light and a secondary ellipsoidal reflector with a high-beam LED array for generating high-beam light. The light emitted from the low-beam LED array device (ray 1) is reflected by the primary ellipsoidal reflector and cut off by the baffle. The low-beam output with a bright or dark edge is then transmitted through the lens to form a cutoff line for the low-beam light. Some of the light emitted from the high-beam LED array device (ray 2) is reflected by the secondary ellipsoidal reflector and the top surface of the baffle. This reflected light is then transmitted through the lens to illuminate the upper half region for generating high-beam light. In addition, some of the light emitted from the high-beam LED array device (ray 3) is reflected by the primary ellipsoidal reflector and then transmitted through the lens to illuminate the lower-half region for generating high-beam light. Thus, the illumination requirements of high-beam light can be achieved with the high-beam LED array device alone. The proposed compound ellipsoidal reflector design can be achieved using two simple ellipsoidal reflectors and a conventional condenser lens instead of a condenser lens with a complex surface. By using a projector-type structure with a specific condenser lens and baffle plate, the design of a single headlamp producing low- and high-beam light can meet the ECE R112 requirements. Photonics 2021, 8, 32 4 of 13 Photonics 2021, 8, 32 4 of 13

Figure 1. The structure of the single headlamp with low- and high-beam light in this study. Figure 1. The structure of the single headlamp with low- and high-beam light in this study.

2.2. Proposed Proposed Design Design Process Process and and Simulation Simulation Results AA single projector-type headlamp headlamp generati generatingng both both low- low- and and high-beam high-beam light light is is ex- ex- pected to provideprovide aa low-beam low-beam cutoff cutoff line line for for low-beam low-beam light light and and bright, bright, centrally centrally distributed distrib- utedlight light with with no particular no particular control control for high-beam for high-beam light light to meet to meet the ECE the ECE R112 R112 regulations. regulations. The Theproposed proposed headlamp headlamp comprises comprise a compounds a compound ellipsoidal ellipsoidal reflector, reflector, a baffle, a baffle, a condenser a condenser lens, lens,and low-and andlow- high-beam and high-beam LED array LED devices array devices (Figure 1(Figure). For generating 1). For generating low-beam low-beam light, the light,LED lightthe LED sources light in sources the proposed in the headlampproposed areheadlamp positioned are atpositioned the first focal at the point first (F focal1) of pointthe ellipsoidal (F1) of the reflector. ellipsoidal The reflector. light generated The light from generated the LED from source the converges LED source to theconverges second tofocal the pointsecond (F 2focal) after point being (F reflected2) after being by the reflected ellipsoidal by the reflector. ellipsoidal Then, reflector. the projector Then,lens the projectorwith the overlappedlens with the second overlapped focal point second of thefoca ellipsoidall point of the reflector ellipsoidal projects reflector the light projects from thethe light ellipsoidal from the reflector ellipsoidal at a certain reflector distance. at a certain Thus, thedistance. designs Thus, of the the compound designs of ellipsoidal the com- poundreflector ellipsoidal and baffle reflector plate as and well baffle as the plate choice as ofwell the as condenser the choice lens of the and condenser LED array lens devices and LEDplay array crucial devices roles in play the proposedcrucial roles headlamp in the proposed structure. headlamp structure.

2.1.2.1. Design Design of of the the Primary Primary Ellipsoidal Ellipsoidal Reflector Reﬂector for Low-Beam Light TheThe ellipsoidal reflector reﬂector for the LED projec projector-typetor-type headlamp is based on the basic principle of elliptical design. The elliptic ellipticalal equation can be expressed as follows: x2 y2 ++ ==11 (1) a2 b2

where 2a and 2b are the major and minor axes of the ellipse, respectively, and F1 and F2 where 2a and 2b are the major and minor axes of the ellipse, respectively, and F1 and F2 are arethe firstthe first and and second second focal focal points points of the of ellipse, the ellipse, respectively. respectively. Figure 2Figure illustrates 2 illustrates the defined the 1 2 definedfirst focal first length focal (f length1) and (f second) and second focal length focal (flength2) of the (f ) ellipse,of the ellipse, which canwhich be can expressed be ex- pressedas follows: as follows: f1 = a − c (2) f =a−c (2) f2 = a + c (3) f =a+c (3) where c is the linear eccentricity of the ellipse and can be expressed as follows: where c is the linear eccentricity of the ellipse and can be expressed as follows: 2 2 2 c ==aa −−bb (4)

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FigureFigure 2. 2.Schematic Schematic of of the the ellipsoid. ellipsoid.

ConsideringConsidering the the limited limited size size of of a a modern modern headlamp, headlamp, the the major major axis axis (a) (a) of of the the primary primary 1 ellipsoidalellipsoidal reflector reflector of of the the proposed proposedheadlamp headlampheadlamp is isis set setset as asas32–39 32–3932–39 mm mmmmand andandf 1ff1 is isis set setset as asas 10 1010 mm. mm.mm. 2 FromFrom Equations Equations (2)–(4), (2)–(4), the the values values of b,of c, b, and c, and f2 can f 2 becancan calculated bebe calculatedcalculated for the forfor primary thethe primaryprimary ellipsoidal ellip-ellip- reflectorsoidal reflector (Table1 ).(Table Figure 1).3 Figureillustrates 3 illustrate the correspondings the corresponding ellipsoidal ellipsoidal reflectors reflectors used in theused proposedinin thethe proposedproposed headlamp headlampheadlamp for generating forfor generatinggenerating low-beam low-beamlow-beam light. light.light.

TableTable 1. 1.Parameters Parameters of of the the primary primary ellipsoidal ellipsoidal reﬂectors reflectors used used in in this this study. study.

a(mm) a(mm)a (mm) c(mm)c(mm) c (mm) b(mm)b(mm) b (mm) f1(mm) f1(mm) f1 (mm) f2f2(mm) f2(mm) (mm) NO.1NO.1 38.5 38.5 28.5 28.5 25.87 25.87 10 10 67 67 NO.2NO.2 37 37 27 27 25.29 25.29 10 10 64 64 NO.3 35.5 25.5 24.64 10 61 NO.3 35.5 25.5 24.64 10 61 NO.4NO.4 34 34 24 24 24.04 24.04 10 10 58 NO.4NO.5 34 32.5 24 22.5 24.04 23.44 10 10 55 58 NO.5 32.5 22.5 23.44 10 55

FigureFigure 3. 3.Schematic Schematic cross-sectional cross-sectional views views of of primary primary ellipsoidal ellipsoidal reﬂector reflector Nos. Nos. 1 1 to to 5. 5.

ForFor generating generating low-beam low-beam lightlight byby using using the the proposed proposed headlamp, headlamp, the the bafﬂe baffle plate plate is is designeddesigned to to hold hold the the light light emitted emitted from from the the low-beam low-beamlow-beam LED LEDLED array arrayarray device devicedevice on onon the thethe top toptop surface surfacesurface

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ofof the the plate plate and and provide provide the the required required cutoff cutoff line line by by regulating regulating the the Z-shape Z-shape prominent prominent in in frontfront of of the the plate, plate, as as shown shown in in Figure Figure4 .4. To To project project the the light light from from the the Z-shaped Z-shaped prominent prominent bafflebaffle at at a a distance, distance, a a projector projector lens lens with with commercial commercial specifications specifications (diameter (diameter of of 71 71 mm mm andand focal focal length length of of 42 42 mm) mm) is is used. used. The The material material of of the the projector projector lens lens is is selected selected as as Schott Schott BK7BK7 glass.glass. TheThe reflectivityreflectivity ofof thethe bafflebaffle plate plate and and ellipsoidal ellipsoidal reflector reflector are are assumed assumed to to be be 0.90.9 [[17].17]. An LED LED array array device device of of OSLON OSLON Black Black Flat Flat S (KW S (KW HJL531.TE, HJL531.TE, OSRAM OSRAM Opto Opto Sem- Semiconductors)iconductors) is used is used to design to design the headlamp the headlamp generating generating bothboth low- low-and high-beam and high-beam light. light.OSLON OSLON Black Black Flat S Flat (KW S HJL531.TE) (KW HJL531.TE) is a thre is ae-chip three-chip LED device LED device packed packed with three with power three powerchips (1 chips × 1 (1mm)× 1 on mm) a ceramic on a ceramic board. board. By using By usingthe Rayfile the Rayfile of KW of HJL531, KW HJL531, the LED the LEDarray arraydevice device with withan output an output power power of 700 of lm 700 is lmpositioned is positioned at F1 of at the F1 of primary the primary ellipsoidal ellipsoidal reflec- reflector.tor. To validate To validate the effectiveness the effectiveness of the of prop theosed proposed design design with different with different ellipsoidal ellipsoidal reflec- reflectors,tors, the commercial the commercial software software TracePro TracePro for forMonte Monte Carlo Carlo rayray tracing tracing method method is used is used for forsimulating simulating the the illuminance illuminance distribution distribution in in a adetection detection plane plane placed placed 25 m inin frontfront ofof the the low-beamlow-beam LED LED headlamp. headlamp.

FigureFigure 4. 4.The The structure structure of of the the projector-type projector-type LED LED headlamp headlamp in in this this study. study.

FigureFigure5 a5a displays displays the the simulated simulated illuminance illuminance distribution distribution of of the the low-beam low-beam headlamp headlamp withwith primary primary ellipsoidal ellipsoidal reflector reflector No. No. 1, 1, whose whose cutoff cutoff line line meetsmeets thethe ECEECE R112R112 regulation.regulation. FigureFigure6 6depicts depicts the the simulated simulated illuminances illuminances of of the the low-beam low-beam headlamps headlamps with with primary primary ellipsoidalellipsoidal reflectorreflector Nos.Nos. 11 toto 55 atat the the test test points points on on the the detection detection plane. plane. In In Figure Figure6 ,6, the the greengreen lineslines represent the minimum minimum required required valu valueses at atthe the test test points points according according to the to ECE the ECER112 R112 regulation, regulation, and the and red the lines red linesrepresen representt the maximum the maximum required required values. values. The illumi- The illuminancesnances at all atthe all test the points test points except except certain certain ones, ones,such suchas 75R, as 50R, 75R, 50V, 50R, 25L, 50V, and 25L, 25R, and 25R,cross crossthe green the green lines, lines,which which indicates indicates that most that of most the illuminances of the illuminances meet the meet ECE the R112 ECE require- R112 requirement.ment. Moreover, Moreover, the illuminances the illuminances of the of75L the an 75Ld 50L and test 50L points test pointscross the cross red the lines. red There- lines. Therefore,fore, the illuminances the illuminances at the at the bright bright center center exceed exceed the the ECE ECE R112 R112 requirement, whereaswhereas thosethose at at the the test test points points fail fail to to meet meet the the requirement.requirement. For For the the projector-typeprojector-type headlamps headlamps with with symmetricalsymmetrical ellipsoidal ellipsoidal reflectors, reflectors, the the projected projecte lightd light at at the the center center of theof the detection detection plane plane is excessivelyis excessively high high for for the the low-beam low-beam headlamp headlamp requirement. requirement. Moreover, Moreover, thespill the spill zone zone on the on detectionthe detection plane plane is excessively is excessively dark. dark. An illuminanceAn illuminance distribution distribution with with a wide a wide horizontal horizon- spreadtal spread onthe on detectionthe detection plane plane can can illuminate illuminate the the broad broad light light area area and and provide provide not not only only a suitablea suitable center center light light but but also also sufficient sufficient illuminance illuminance in in the the spill spill zone. zone. To To achieve achieve a a wide wide horizontalhorizontal spread, spread, the the lateral lateral expansion expansion of of a 2-mm-longa 2-mm-long ellipsoidal ellipsoidal reflector reflector can can be used,be used, as shownas shown in Figure in Figure7. For 7. the For lateral the lateral expansion expansion of the primaryof the primary ellipsoidal ellipsoidal reflector, reflector, it is desired it is

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desiredto concentrating to concentrating more light more emitting light emitting form the formform LED arraythethe LEDLED device arrayarray through devicedevice the throughthrough condenser thethe con-con- lens denserto illuminate lens to the illuminate region for the low-beam region for light. low-be Thus,am light. the ellipsoidal Thus, the reflector ellipsoidal No. reflector 1 with large No. 1size with is large chosen size to is be chosen with a to lateral be with expansion. a lateral Figureexpansion.5b displays Figurethe 5b displays simulateddisplays thethe illuminance simulatedsimulated illuminanceilluminancedistribution distributiondistribution of the low-beam ofof thethe headlamp low-beamlow-beam with headlampheadlamp laterally withwith expanding laterallylaterally ellipsoidal expandingexpanding reflector ellipsoidalellipsoidal No. reflector1. A wide No. horizontal 1. A wide spreadhorizontal on thespread detection on thethe plane detectiondetection can planeplane be achieved cancan bebe achievedachieved using the usingusing laterally thethe laterallylaterallyexpanding expandingexpanding ellipsoidal ellipsoidalellipsoidal reflector. reflector.reflector.

((a)) ((b)) FigureFigure 5. Simulated illuminanceilluminance distributionsdistributions of of low-beam low-beam headlamps headlamps with with the the (a ()a symmetrical)) symmetricalsymmetrical ellipsoidal ellipsoidalellipsoidal reﬂector reflectorreflector and andand (b) ((expandingb)) expandingexpanding ellipsoidal ellipsoidalellipsoidal reﬂector. reflector.reflector.

Figure 6. The simulated illuminances of the low-beam headlamps with primaryprimary ellipsoidalellipsoidal reflectorreflector Nos.Nos. 11 toto 55 atat thethe testtest Figure 6. The simulated illuminances of the low-beam headlamps with primary ellipsoidal reﬂector Nos. 1 to 5 at the test points on the detection plane. points on the detection plane.

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FigureFigure 7. 7.The The low-beam low-beam headlamp headlamp with with laterally laterally expanding expanding ellipsoidal ellipsoidal reﬂector reflector No. 1. No. 1.

2.2.2.2. Design Design of of the the Secondary Secondary Ellipsoidal Ellipsoid Reflectoral Reflector (ER) for(Er) High-Beam for High-Beam Light Light ToTo obtain obtain a single a single headlamp headlamp with with both low-both andlow- high-beam and high-beam light, a compoundlight, a compound ER ER composed of two simple ERs is used. The secondary ER concentrates the light generated composed of two simple ERs is used. The secondary ER concentrates the light generated by the high-beam LED array device onto its second focal point. By using a baffle plate andby primarythe high-beam ER, the lightLED generatedarray device from onto the high-beam its second LED focal array point. device By using can be a directed baffle plate and andprimary transmitted ER, the through light generated a specific condenser from the lenshigh to-beam illuminate LED array the region device for can high-beam be directed and light.transmitted The compound through ER a comprisesspecific condenser a primary ERlens and to illuminate secondary ER. the The region front for part high-beam of the light. compoundThe compound ER is the ER primary comprises ER, which a primary generates ER low-beamand secondary light, whereas ER. The the front back part part of is the com- thepound secondary ER is ER, the which primary generates ER, which high-beam generates light. For low-beam designing light, the compound whereas reflector, the back part is thethe back secondary part of theER, primary which generates ER is removed high-beam and replaced light. byFor the designing secondary the reflector, compound as reflec- showntor, the in back Figure part1. For of the the projector-type primary ER LEDis remo headlamp,ved and some replaced of the by light the emitted secondary from reflector, theas low-beamshown in LED Figure array 1. device, For the which projector-type is reflected fromLED theheadlamp, back part ofsome the primaryof the light ER, emitted contributes less to the illuminances at the test points and zone of the low-beam LED than from the low-beam LED array device, which is reflected from the back part of the primary the ECE requirement, as shown in Figure8. Figure9 illustrates the simulated illuminance distributionsER, contributes of this less reflector to the with illuminances and without at the the back test part, points which and are zone found of to the be similar.low-beam LED Althoughthan thethe ECE illuminance requirement, without as shown the back in part Figure is lower 8. Figure than that 9 illustrates with it, all the illuminances simulated illumi- atnance the test distributions points and zones of this of reflector the primary with ERs and without without the the back back part part, still which meet the are low- found to be beamsimilar. ECE Although requirement. the Therefore, illuminance a 5-cm-long without partthe isback removed part is from lower the than back that of primary with it, all illu- ERminances No. 1 and at connected the test points to the secondaryand zones ER. of Thethe primary depth of theERs hole without made inthe this back reflector part still meet isthe calculated low-beam to be ECE 12.749 requirement. mm by using Therefore, Equation (1). a 5-cm-long part is removed from the back of primaryIn this ER study, No. the 1 and secondary connected ER concentrates to the secondary the light emittedER. The from depth the of high-beam the hole LED made in this array device onto its second focal point. The light hitting this point is reflected by the baffle reflector is calculated to be 12.749 mm by using Equation. (1). plate and directed through the lens to illuminate the region for high-beam light. However, the high-beam lighting should meet the ECE requirements. Thus, the light reflected by the baffle plate and directed through the lens should contribute to the illuminances at the specific points on the detection plane. According to the photometric requirements of high-beam light in the ECE R112 regulation, a light pattern with a large area should be formed. Therefore, the second focal point of the secondary ER for high-beam light should be away from the focal point of the lens, as shown in Figure 10. Consequently, the positions of the secondary ER and high-beam LED array device should be defined. Considering the size limitation of the compact headlamp, the length of the secondary ER should be less than 10 mm. Thus, the distance from the end of the secondary ER to that of the primary reflector is set as 10 mm. In other words, the distance from the end of the secondary ER to that of the primary reflector without the 5-cm-long back part is set as 15 mm. Moreover, the high-beam LED array device should be covered by the secondary ER to the maximum

Figure 8. The structure of the projector-type LED headlamp in this study. Some of the light reflected from the back part of primary ellipsoidal reflector contributes less to the illuminances for low-beam regulation requirement.

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Figure 7. The low-beam headlamp with laterally expanding ellipsoidal reflector No. 1.

2.2. Design of the Secondary Ellipsoidal Reflector (Er) for High-Beam Light To obtain a single headlamp with both low- and high-beam light, a compound ER composed of two simple ERs is used. The secondary ER concentrates the light generated by the high-beam LED array device onto its second focal point. By using a baffle plate and primary ER, the light generated from the high-beam LED array device can be directed and transmitted through a specific condenser lens to illuminate the region for high-beam light. The compound ER comprises a primary ER and secondary ER. The front part of the compound ER is the primary ER, which generates low-beam light, whereas the back part is the secondary ER, which generates high-beam light. For designing the compound reflector, the back part of the primary ER is removed and replaced by the secondary reflector, Photonics 2021, 8, 32 as shown in Figure 1. For the projector-type LED headlamp, some of the 9light of 13 emitted from the low-beam LED array device, which is reflected from the back part of the primary ER, contributes less to the illuminances at the test points and zone of the low-beam LED possiblethan the extent. ECE requirement, The first focal lengthas shown (f1) ofin theFigure secondary 8. Figure ER should9 illustrates be small. the Thus,simulated this illumi- lengthnance is distributions set as 5 mm, andof this the reflector high-beam with LED and array without is positioned the back at the part, first which focal point are found of to be thesimilar. secondary Although ER. After the selectingilluminance the positionwithout and the firstback focal part length is lower of the than secondary that with ER, it, all illu- theminances second focalat the point test points of the secondary and zones reflector of the primary can be defined ERs without according the to back its second part still meet focal length (f ). In addition, the distance between the second focal point of the secondary the low-beam2 ECE requirement. Therefore, a 5-cm-long part is removed from the back of ER and the focal point of the lens is determined. To fit the height of the removed back partprimary of the ER main No. second 1 and ER connected and due toto thethe size secondary limitation, ER. the The second depth focal of the length hole of made the in this secondaryreflector is ER calculated is set as 57 to mm. be 12.749 mm by using Equation. (1).

Figure 8. The structure of the projector-type LED headlamp in this study. Some of the light re- Figure 8. The structure of the projector-type LED headlamp in this study. Some of the light reﬂected flected from the back part of primary ellipsoidal reflector contributes less to the illuminances for Photonics 2021, 8, 32 from the back part of primary ellipsoidal reﬂector contributes less to the illuminances for low-beam9 of 13 low-beam regulation requirement. regulation requirement.

(a) (b)

FigureFigure 9.9. SimulatedSimulated illuminanceilluminance distributionsdistributions ofof thethe primaryprimary ERER No.No. 11 ((aa)) withwith andand ((bb)) withoutwithout thethe backback part.part.

In this study, the secondary ER concentrates the light emitted from the high-beam LED array device onto its second focal point. The light hitting this point is reflected by the baffle plate and directed through the lens to illuminate the region for high-beam light. However, the high-beam lighting should meet the ECE requirements. Thus, the light reflected by the baffle plate and directed through the lens should contribute to the illuminances at the specific points on the detection plane. According to the photometric requirements of high-beam light in the ECE R112 regulation, a light pattern with a large area should be formed. Therefore, the second focal point of the secondary ER for high-beam light should be away from the focal point of the lens, as shown in Figure 10. Consequently, the positions of the secondary ER and high-beam LED array device should be defined. Considering the size limitation of the compact headlamp, the length of the secondary ER should be less than 10 mm. Thus, the distance from the end of the secondary ER to that of the primary reflector is set as 10 mm. In other words, the distance from the end of the secondary ER to that of the primary reflector without the 5-cm-long back part is set as 15 mm. Moreover, the high-beam LED array device should be covered by the secondary ER to the maximum possible extent. The first focal length (f1) of the secondary ER should be small. Thus, this length is set as 5 mm, and the high-beam LED array is positioned at the first focal point of the secondary ER. After selecting the position and first focal length of the secondary ER, the second focal point of the secondary reflector can be defined according to its second focal length (f2). In addition, the distance between the second focal point of the secondary ER and the focal point of the lens is determined. To fit the height of the removed back part of the main second ER and due to the size limitation, the second focal length of the secondary ER is set as 57 mm.

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FigureFigure 10. 10.The The design design of of the the secondary secondary ellipsoidal ellipsoidal reﬂector reflector in in this this study. study. Figure 10. The design of the secondary ellipsoidal reflector in this study. 3.3. Experimental Experimental Implementation Implementation and and Discussion Discussion 3. Experimental Implementation and Discussion InIn this this study, study, Monte Monte Carlo Carlo ray ray tracing tracing simulations simulations were were performed performed to to conﬁrm confirm the the In this study, Monte Carlo ray tracing simulations were performed to confirm the opticaloptical characteristics characteristics of of the the proposed proposed novel novel design design of of a a single single headlamp headlamp generating generating both both optical characteristics of the proposed novel design of a single headlamp generating both low-low- and and high-beam high-beam light.light. A A low-beam low-beam LED LED array array device device with with a atotal total output output power power of 700 of low- and high-beam light. A low-beam LED array device with a total output power of 700 700lm lmwas was positioned positioned at atF1 Fof1 ofthe the primary primary ellipsoidal ellipsoidal reflector,reflector, and and a high-beam LEDLED array array lm was positioned at F1 of the primary ellipsoidal reflector, and a high-beam LED array devicedevice with with a totala total output output power power of 1050of 1050 lm waslm was positioned positioned at F1 atof F the1 of secondary the secondary ellipsoidal ellip- device with a total output power of 1050 lm was positioned at F1 of the secondary ellip- reflector.soidal reflector. The target The planetarget was plane placed was plac 25 med from 25 m the from lens. the Thelens. simulated The simulated illuminance illumi- soidal reflector. The target plane was placed 25 m from the lens. The simulated illumi- distributionnance distribution of the low-beam of the low-beam light in the light target in planethe target is shown plane in isFigure shown 11 in, and Figure the simulated11, and the nance distribution of the low-beam light in the target plane is shown in Figure 11, and the andsimulated measured and illuminances measured illuminances are listed in are Table listed2. The in illuminanceTable 2. The distributionilluminance ofdistribution the low- simulated and measured illuminances are listed in Table 2. The illuminance distribution beamof the light low-beam generated light by generated the proposed by the headlamp proposed with headlamp only the with low-beam only the LED low-beam array device LED of the low-beam light generated by the proposed headlamp with only the low-beam LED hasarray a cutoff device line has meeting a cutoff the line ECE meeting requirement. the ECE In requirement. addition, all In illuminances addition, all of illuminances each point arrayand line device meet has the a ECE cutoff R112 line regulation meeting the for ECE low-beam requirement. light. In addition, all illuminances of each point and line meet the ECE R112 regulation for low-beam light. of each point and line meet the ECE R112 regulation for low-beam light.

Figure 11. Simulated illuminance distribution of the low-beam light generated by the proposed Figure 11. Simulated illuminanceilluminance distribution distribution of theof the low-beam low-beam light light generated generated by the by proposed the proposedheadlamp. headlamp. headlamp.

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Table 2. Comparison of the simulated and measured illuminances of the LED headlamp with the corresponding values set byTable the ECE 2. Comparison R112 regulation of the (Class simulated B) for and low-beam measured light. illuminances of the LED headlamp with the corresponding values set by the ECE R112 regulation (Class B) for low-beam light. Point on Measuring Screen Required Illuminance in Lux Simulated Illuminance in Lux Measured Illuminance in Lux Point on B50LMeasuring Screen Required ≤Illuminance0.4 in Lux Simulated Illuminance 0.08 in Lux Measured Illuminance 0.19 in Lux 75RB50L ≥12≤0.4 13.700.08 13.34 0.19 75L75R ≤12≥12 10.6613.70 9.6613.34 50L75L ≤15≤12 13.6110.66 12.869.66 50R50L ≥12≤15 14.5913.61 13.2612.86 50V50R ≥6≥12 14.2514.59 13.9213.26 25L50V ≥2≥6 12.5114.25 12.1913.92 25R25L ≥2≥2 11.5212.51 11.3512.19 zone25R I ≤2 E*≥2 OK11.52 OK11.35 Ⅰ zonezone III ≤0.7≤2 E* OK OK OK OK Ⅲ zonezone IV ≥3≤0.7 OKOK OK OK zone Ⅳ ≥3 OK OK E* is the actually measured value in point 50R. For the generation of high-beam light by using the proposed headlamp, a high-beam For the generation of high-beam light by using the proposed headlamp, a high-beam LED array device with a total output power of 1050 lm is positioned at F1 of the secondary LED array device with a total output power of 1050 lm is positioned at F1 of the secondary ellipsoidalellipsoidal reﬂector.reflector. TheThe simulated simulated illuminance illuminancedistribution distributionof ofthe the low-beam low-beam light light in in the the targettarget planeplane is is depicted depicted in in Figure Figure 12 12,, and and the the simulated simulated and and measured measured illuminances illuminances are are listedlisted inin TableTable3 .3. The The illuminance illuminance distribution distribution of of the the high-beam high-beam light light generated generated by by the the proposedproposed headlamp headlamp with with only only the the high-beam high-beam LED LED array array device device forms forms a a light light pattern pattern with with aa large large area, area, and and all all illuminances illuminances at at each each point point and and line line meet meet the the ECE ECE R112 R112 regulation regulation for for high-beamhigh-beam light. light.

FigureFigure 12.12. SimulatedSimulated illuminance illuminance distribution distribution of the of high-beam the high-beam light lightgenerated generated by the byproposed the proposedheadlamp. headlamp.

TableTable 3. 3.Comparison Comparison of of the the simulated simulated and and measured measured illuminances illuminances of of the the novel novel single single headlamp headlamp with with the the corresponding corresponding valuesvalues set set by by ECE ECE R112 R112 for for high-beam high-beam light. light. Required Illuminance in Simulated Illuminance in Measured Illuminance in PointPoint on Measuring on Measuring Screen Screen Required Illuminance in Lux Simulated Illuminance in Lux Measured Illuminance in Lux Lux Lux Lux Emax ≥48 & ≤240 52.18 51.75 Point HVEmax ≥0.8Emax≥48 & ≤240 41.7452.18 39.36 51.75 Point HV toPoint 1125L HV and R ≥24≥0.8Emax 30.6941.74 28.65 39.36 PointPoint HV toHV 2250L to 1125L and R and R ≥6≥24 17.4730.69 15.628.65 Point HV to 2250L and R ≥6 17.47 15.6 To verify the effectiveness of the proposed design, a prototype of the proposed head- lampTo was verify developed, the effectiveness as depicted of the in Figure proposed 13. Fordesign, the a generation prototype ofof low-beamthe proposed light head- by lamp was developed, as depicted in Figure 13. For the generation of low-beam light by using the proposed headlamp, the OSLON Black Flat S device (KW HJL531.TE, OSRAM

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using the proposed headlamp, the OSLON Black Flat S device (KW HJL531.TE, OSRAM OptoOpto Semiconductors)Semiconductors) waswas positionedpositioned atat thethe firstfirst focalfocal pointpoint of of the the primary primary ellipsoidal ellipsoidal reflectorreflector andand operatedoperated at at 8.795 8.795 V V and and 0.5 0.5 A Awith with an anoutput output of 700 of 700 lm. lm.For generating For generating high- high-beambeam light lightby using by using the proposed the proposed headlamp headlamp,, the OSLON the OSLON Black Black Flat S Flat device S device was wasposi- positionedtioned at the at first the firstfocal focal point point of the of secondary the secondary ellipsoidal ellipsoidal reflector reflector and operated and operated at 9.339 at V 9.339and 1.083 V and A 1.083with Aan withoutput an of output 1050 lm. of 1050 The lm.luminous The luminous intensity intensitydistribution distribution of the head- of thelamp headlamp with only with low- only or low-high-beam or high-beam light was light measured was measured using a using goniophotometer a goniophotometer (GMS- (GMS-1800C;1800C; SENSING). SENSING). The measurement The measurement results results are listed are listedin Tables in Tables 2 and2 3. and All3 .the All illumi- the illuminancesnances of each of each point point and and line line met met the the ECE ECE R112 R112 requirements requirements for for low- andand high-beamhigh-beam light.light. However,However, thethe measuredmeasured illuminancesilluminances ofof eacheach pointpoint andand lineline inin TablesTables2 2and and3 are3 are lowerlower than than the the simulated simulated ones. ones. TheThe reductionreduction ofof thethe outputoutput powerspowers ofof thethe low-low- andand high-high- beambeam LEDLED arraysarrays owingowing toto the the heat heat is is believed believed to to be be responsible responsible for for the the lower lower measured measured illuminancesilluminances of of each each point point and and line line than than the the simulated simulated ones. ones.

FigureFigure 13. 13.Prototype Prototype sample sample of of the the proposed proposed headlamp. headlamp.

4.4. ConclusionsConclusions ThisThis paperpaper proposesproposes aa novel novel design design of of a a single single headlamp headlamp generating generating both both low- low- and and high-beamhigh-beam lightlight toto meetmeet thethe ECE ECE R112 R112 regulation. regulation. TheTheproposed proposedheadlamp headlamp adoptsadopts thethe structurestructure of of the the projector-typeprojector-type headlamp headlamp andand comprisescomprises aa compoundcompound ellipsoidalellipsoidal reflector,reflector, aa bafflebaffle plate, plate, a a condenser condenser lens, lens, and and LED LED array array devices devices generating generating low- low- and and high-beam high-beam light.light. The compound compound ellipsoidal ellipsoidal reflector reflector comp comprisesrises a primary a primary ellipsoidal ellipsoidal reflector reflector for gen- for generatingerating low-beam low-beam light light and and a asecondary secondary ellip ellipsoidalsoidal reflector reflector for generatinggenerating high-beamhigh-beam light.light. TheThe light emitted emitted from from the the low- low- and and high high-beam-beam LED LED array array devices devices is reflected is reflected by bythe theprimary primary and and secondary secondary ellipsoidal ellipsoidal reflectors, reflectors, respectively, respectively, and transmitted throughthrough thethe condensercondenser lens lens to to illuminate illuminate the the detection detection plane. plane. Monte Monte Carlo Carlo ray tracing ray tracing simulations simulations were performedwere performed to confirm to confirm the optical the optical characteristics characteristics of the of proposed the proposed design. design. The simulation The simu- resultslation results of the low-beamof the low-beam light with light only with the only low-beam the low-beam LED arrayLED array device device show show that thethat proposedthe proposed headlamp headlamp created created a correct a correct light li patternght pattern and performedand performed an obvious an obvious cutoff cutoff line. Allline. the All simulated the simulated illuminances illuminances of each of point each metpoint the met ECE the R112 ECEregulation R112 regulation for low-beam for low- light.beam Moreover,light. Moreover, the simulation the simulation results results of the high-beamof the high-beam light with light only with the only high-beam the high- LEDbeam array LED device array device formed formed a light a pattern light pattern with a with large a area.large Inarea. addition, In addition, all the all simulated the simulated illuminances of each point and line met the ECE R112 regulation for high-beam light.

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illuminances of each point and line met the ECE R112 regulation for high-beam light. A prototype of the proposed headlamp was also developed to verify the design’s effectiveness. By using the low-beam LED array device of merely 4.397 W, the measured illuminance distributions of the low-beam light can reach the illuminances of each point met the ECE R112 regulation for low-beam light. Additionally, the measured illuminance distributions of the high-beam light can reach the illuminances of each point and line met the ECE R112 regulation for high-beam light when the high-beam LED array device of merely 10.11 W was used. As a result, the proposed headlamp in this study is feasible for the application of single headlamp generating both low- and high-beam light.

Author Contributions: Conceptualization, S.-P.Y. and C.-Y.Y.; methodology, B.-M.C.; software, C.-Y.Y.; validation, S.-P.Y. and B.-M.C.; formal analysis, H.-K.F.; investigation, H.-K.F.; data curation, H.-K.F.; writing—original draft preparation, B.-M.C. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Informed consent was obtained from all subjects involved in the study. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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