micromachines Article Asymmetric Double Freeform Surface Lens for Integrated LED Automobile Headlamp Hui Zhang 1, Dengfei Liu 1,2, Yinwan Wei 1,2 and Hong Wang 1,2,* 1 Engineering Research Center for Optoelectronics of Guangzhou Province, School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510640, China; [email protected] (H.Z.); eedfl[email protected] (D.L.); [email protected] (Y.W.) 2 Guangdong Provincial Engineering Research Center for Wide Bandgap Semiconductor Chips and Application, Zhongshan Institute of Modern Industrial Technology, South China University of Technology, Zhongshan 528437, China * Correspondence: [email protected]; Tel.: +86-20-87111557 Abstract: We propose a design method of asymmetric double freeform surface lens for an integrated LED automobile headlamp and develop an integrated LED automobile optical system. A single asymmetric double freeform surface lens is designed to redistribute rays emitting from the light source for realizing both low and high beams. Moreover, a freeform surface reflector is used to improve the energy efficiency of high beams. The prism placed in the optical path can suppress chromatic dispersion on the edge of the target plane. Simulation and experimental results show that the illumination values and color temperature of the key points can fully meet the requirements of United Nations Economic Commission for Europe vehicle regulations (ECE) R112, 48, and 128. The volume of the whole optical system comprised of freeform surface elements is smaller than that of the low beam system of a traditional headlamp, resulting in saved space, in which other electronic Citation: Zhang, H.; Liu, D.; Wei, Y.; devices can be installed for the safety of the driver, which indicates that the proposed method is Wang, H. Asymmetric Double practical in the field of automobile lighting. Freeform Surface Lens for Integrated LED Automobile Headlamp. Micromachines 2021, 12, 663. https:// Keywords: asymmetric double freeform surface lens; LED; integrated automobile headlamp; freeform doi.org/10.3390/mi12060663 surface optics Academic Editors: W.B. Lee and Lihua Li 1. Introduction Received: 5 May 2021 LEDs have gradually entered our lives due to their advantages of energy saving, Accepted: 4 June 2021 high energy efficiency, long lifespan, and miniaturization [1,2]. In the past decade, LEDs Published: 5 June 2021 have been used increasingly as light sources in automobile headlamps for their excellent properties [3–6]. Since low-beam requirements are completely different from those of high Publisher’s Note: MDPI stays neutral beams, the traditional optical systems of low and high beams in headlamps are designed with regard to jurisdictional claims in separately, mainly including projection and reflection types. In general, projection-type published maps and institutional affil- optical systems deflect by lenses and reflection type by reflectors [7]. It is easy to form iations. a clear cutoff line but hard to improve the energy efficiency for projection types with a baffle plate; conversely, the reflection type without a baffle plate is more efficient but has a dim cutoff line. Previously, Cvetkovic et al. presented a simultaneous multiple surface (SMS) 3D method for automobile low and high beam headlamps, whose optical efficiency Copyright: © 2021 by the authors. is more than 75% [8,9]. Domhardt et al. designed a combined lens for LED-based low Licensee MDPI, Basel, Switzerland. beam headlamp but needed large space to install lenses for high energy efficiency [10]. This article is an open access article Ge et al. used an elliptical and parabolic reflector to design a low beam headlamp that distributed under the terms and had high energy efficiency [5]. Hsieh et al. proposed a modular design for an LED conditions of the Creative Commons vehicle projector headlamp that provided the cutoff line of low beams without a baffle Attribution (CC BY) license (https:// plate [11]. Chu et al. proposed a low beam headlamp with a compound ellipsoidal reflector creativecommons.org/licenses/by/ that achieved the highest energy efficiency in the existing literature [12]. In the past, 4.0/). Micromachines 2021, 12, 663. https://doi.org/10.3390/mi12060663 https://www.mdpi.com/journal/micromachines Micromachines 2021, 12, 663 2 of 16 our research group has proposed several optical systems for headlamps. For example, an optical system with a single freeform surface lens [13], a low chromatic dispersion headlamp system using a parabolic reflector and micro-lens array [14], a LED motorcycle headlight using a combined lens [15], etc. More separate design methods for low and high beams can be found in references [16–21]. In recent years, compact headlamp design has become more and more fashionable [22]. The integrated headlamp reduces its volume by sharing some optical elements between low- and high-beam systems, allowing the designs of integrated headlamps to fit with the trend of compact design. However, few studies in the literature have been reported about the integrated headlamp. Hung et al. designed an integrated headlamp incorporating a digital micromirror device [23]. Wu et al. presented a modular LED headlamp system based on a freeform reflector [24]. Borocki et al. recommended a single optical system with both a low beam and a high beam, in which switching between the low beam and high beam was achieved by a removable shutter [25]. M. Rice et al. proposed an integrated headlamp based on a projective low- beam system, in which the light emitted from the high-beam source was reflected by the lower plane of the baffle plate and deflected by the lens to form the illumination distribution of high beams [26]. In previous studies, most of the headlamps were designed individually, which may increase the complexity and volume of the headlamp. Existing integrated headlamps with a removable shutter may affect the reliability of the headlamp. Therefore, it is necessary to study a simple and small-volume headlamp system. In this paper, we proposed a method of designing an asymmetric double freeform surface lens (ADFSL) and developed an integrated LED automobile optical system. On the premise of meeting the requirements of ECE R112, 48, and 128 [27–29], this new integrated LED headlamp system can greatly improve the compactness of the optical system and suppress chromatic dispersion at the edge of the target illumination area. Just one lens is needed to achieve low and high beams, which means that this new headlamp system can save a lot of space. A freeform surface reflector focusing light is proposed to improve energy efficiency. Furthermore, a prism is placed in the optical path to reduce the chromatic dispersion further, which can provide comfortable and safe lighting for the driver. Compared to the traditional, separated headlamp and integrated headlamp, the proposed headlamp has only one single lens to achieve low and high beams, reducing the volume of the automobile headlamp. Furthermore, the color distribution on the target plane using ADFSL and prism is more stable. 2. Design Method The optical system of the new integrated headlamp is shown in Figure1. The whole system consists of an ADFSL, a freeform surface reflector, a prism, a baffle, and two LEDs. The optical system of the low beam includes a LED source, an upper half of the ADFSL, and a baffle plate. Correspondingly, the optical system of the high beam comprises a freeform surface reflector, a prism, the lower half of the ADFSL, and a LED source. Rays emitting from the low beam LED source are partially blocked by the baffle plate and then redistributed by the ADFSL, forming a low beam with a clear cutoff line on the target plane. On the other hand, rays from the high beam LED source are focused on a point by the freeform surface reflector and then deflected by the prism. Finally, the remaining rays will be redistributed by the ADFSL to form the illumination distribution of the high beam. The implementation of the low and high beams will be described in detail below. Micromachines 2021, 12, 663 3 of 16 Micromachines 2021, 12, 663 3 of 16 Micromachines 2021, 12, 663 3 of 16 Figure 1. Optical system of the integrated LED automobile headlamp. 2.1. Optical System of the Low Beam Mode Figure 1. Optical system of the integrated LED automobile headlamp. FigureOver 1. Optical the past system decade, of the a series integrated of regulations LED automobile have been headlamp. introduced for driver’s safety. 2.1. Optical System of the Low Beam Mode Low beam is mainly used for good road lighting and cannot cause glare to the opposing 2.1.Over Optical the past System decade, a of series the of Low regulations Beam have Mode been introduced for driver’s safety. drivers.Low beam isAccording mainly used for to good the road ECE lighting R112 and regulations, cannot cause glare the to thetested opposing points and the cutoff line are showndrivers.Over According in Figure the to past the 2. ECE decade, R112 regulations, a series the of tested regulations points and the have cutoff linebeen are introduced for driver’s safety. shown in Figure2. Low beam is mainly used for good road lighting and cannot cause glare to the opposing drivers. According to the ECE R112 regulations, the tested points and the cutoff line are shown in Figure 2. Figure 2. Tested2. Tested points andpoints regions and of low regions beam. of low beam. It can be found that the light shape of the low beam has a wide horizontal spread for both sides,It can which be can found provide that a big the angle light of view shape for drivers. of the Moreover, low thebeam lighting has spot a wide horizontal spread for of the low beam is “dark on the left but bright on the right”.