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— Presentation at IDW '17 —
February 1, 2018
The 24th International Display Workshops (IDW '17) was held at Sendai in Japan from December 6th to 8th. IDW '17 is one of renowned conference about optical technology and applications with about 1,200 participants from worldwide. In this conference, Hitachi, Ltd. gave 4 oral presentations and I gave a presentation about headlamp optical system for integrating high and low beam units corresponding to ADB (Adaptive Driving Beam) titled "Bi-Functional Automotive Headlamps for Adaptive Driving Beam and Low Beam realizing Achromatic Illumination by using a Light Guide."
Our proposed optical system consists of three components; LEDs, a light guide, and a projection lens (Fig. 1). In order to illuminate ADB pattern, we arranged LEDs in an array and turned on and off and used light guide to propagate LED light efficiently. Furthermore, to make integrate high and low beam optical systems, low beam optical system also adopted the configuration using a light guide. Particularly in the low beam, complicated light distribution is required according to the UNECE Regulation No.112, so we reported three ideas driving the design of the low beam light guide in this presentation.
The first idea is to form horizontal light distribution. Low beam illuminates pedestrians in the vicinity of the vehicle, so wide light distribution in the horizontal direction is required. By arranging multiple LEDs in the horizontal direction, optimizing interval of LED and some parameters of the light guide, we realized the light distribution widely illuminated in the horizontal direction (Fig. 2). The second idea is to form vertical light distribution. According to UNECE regulation, it is necessary to illuminate the center of light distribution (correspond to the road far) brightly. Therefore, by changing the slope of the upper surface such that the size of the exit surface increased and the light density reduced, we realized the vertical light distribution (Fig. 3). The third idea is to improve light efficiency. By forming Fresnel structure on the exit surface of the light guide, the light efficiency was improved by 8% (Fig. 4).
We made a prototype that integrates high and low beam units. The design and measured results showed good agreement (Fig. 5), satisfied UNECE Regulation No.112. When a single lens is used for projection lens, chromatic aberration generally occurs, so color blur of cutoff line has been an issue in conventional headlamp unit. In our optical system using the light guide, we confirmed that the color blur of the cutoff line can be drastically reduced because the amount of off-axis rays which has chromatic aberration of the lens can be reduced compared with the conventional unit (Fig. 6).
We will develop the proposed optical configuration further to enhance productivity while continuing discussions with the lamp manufacturer.
(By NAGAYOSHI Mayumi)