E102 Vol. 54, No. 28 / October 1 2015 / Applied Optics Research Article Optical design of an LED motorcycle headlamp with compound reflectors and a toric lens 1 2, 1 1 WEN-SHING SUN, CHUEN-LIN TIEN, *WEI-CHEN LO, AND PU-YI CHU 1Department of Optics and Photonics, National Central University, Chung-Li 32001, Taiwan 2Department of Electrical Engineering, Feng Chia University, Taichung 40724, Taiwan *Corresponding author: [email protected] Received 31 March 2015; revised 16 July 2015; accepted 16 July 2015; posted 28 July 2015 (Doc. ID 236954); published 21 August 2015 An optical design for a new white LED motorcycle headlamp is presented. The motorcycle headlamp designed in this study comprises a white LED module, an elliptical reflector, a parabolic reflector, and a toric lens. The light emitted from the white LED module is located at the first focal point of the elliptical reflector and focuses on the second focal point. The second focal point of the elliptical reflector and the focal point of the parabolic reflector are confocal. We use nonsequential rays to improve the optical efficiency of the compound reflectors. The toric spherical lens allows the device to meet the Economic Commission of Europe, regulation no. 113 (ECE R113). Furthermore, good uniformity is obtained by using aspherical surface optimization of the same toric lens. The reflectivity of the reflector is 95%, and the transmittance of each lens surface is 98%. The average deviation of the high beam is 14.17%, and the optical efficiency is 66.45%. © 2015 Optical Society of America OCIS codes: (080.4228) Nonspherical mirror surfaces; (080.4295) Nonimaging optical systems; (220.2945) Illumination design; (220.4298) Nonimaging optics. http://dx.doi.org/10.1364/AO.54.00E102 1. INTRODUCTION and the other a paraboloid collimating reflector, an off-axis A motorcycle headlamp usually consists of low- and high-beam paraboloid reflector, a baffle, and an imaging lens. The system efficiency of the composite low-beam module reached 58% [8]. lights. Various regulations include certain restrictions for illu- et al. mination requirements. In recent years, with the development Hsieh proposed an LED vehicle projector headlamp sys- of nonimaging optics, some LED headlamp optical design tem, which contained several LED headlamp modules, each of methods based on nonimaging optics have been suggested. which included four components: focused LEDs, asymmetric Herkommer [1] reported on free-form systems as applied to metal-based plates, free-form surfaces, and condenser lenses [9]. imaging and illumination systems. Cvetkovic et al. created a A number of researchers have studied light source modeling to et al. headlamp with one refractive and one reflective free-form sur- simulate various lighting systems. Cassarly measured the face, which produced light with good uniformity and high in- spatial luminance distributions over a range of view angles, tensity [2]. A vehicle headlamp design based on fiber optics and which is an important consideration for lamps in elliptical re- et al. LEDs has also been presented, the intention being to reduce flectors and LEDs [10]. Jenkins rendered the distributive lamp size and heat-dissipation problems. An optical efficiency light for a low-beam headlight design. The challenge here was of 49.4% was obtained for the low beam design [3]. In 2011, to design an efficient lamp package that angularly distributed an LED-based motorcycle headlamp with two horizontal reflec- the flux to meet legal and customer requirements [11]. Zerhau- tors and a light pipe was designed, which had an optical effi- Dreihoefer et al. presented the light source modeling for auto- ciency of about 80% [4]. Chen et al. presented a high-efficiency motive lighting devices and, in the process of calculating and LED headlamp free-form lens design. The free-form lens was simulating automotive lighting devices, used different light separated into low- and high-beam lenses, and the optical effi- source modeling techniques [12]. In this work, we use nonse- ciencies of both lenses were more than 88% [5]. Zhu et al. used quential (NS) rays to improve the optical efficiency of the com- 48 LEDs to build an array with a rectangular beam region pound reflectors. By using a toric lens, we could meet the divided into multiple blocks, each illuminated by an LED. Economic Commission of Europe, regulation no. 113 (ECE In theory, the optical efficiency of the device would exceed R113) and obtain good uniformity. The optical simulation 85% [6]. In 2013, Ge et al. proposed two low-beam systems showed the efficiency of the high beam to be 66.45%, average for an LED-based headlamp architecture, one of which com- deviation 14.17%; the optical efficiency of the low beam was prised an elliptical reflector, a baffle, and a faceted reflector [7], 66.41%, and the average deviation was 13.96%. 1559-128X/15/28E102-07$15/0$15.00 © 2015 Optical Society of America Research Article Vol. 54, No. 28 / October 1 2015 / Applied Optics E103 2. DESIGN METHOD A. Requirements for a High Beam The motorcycle headlamp was designed to conform to ECE R113. The illumination requirements for a high beam projected onto a measuring screen 25 m away from the head- lamp are illustrated in Fig. 1. The irradiated area is 4500 mm × 1000 mm. The height of the HV point is equal to the height of the motorcycle headlamp. The illumination in region B should be greater than 3 lux, while that in region A should be greater than 12 lux. Fig. 2. Requirements for low beam light irradiating the measuring B. Requirements for a Low Beam screen. The illumination requirements for a low beam projected on a measuring screen are shown in Fig. 2. Point HV indicates the height between the headlamp and the road. Point 50 V is lo- cated 375 mm below point HV. The illumination in region A should be greater than 1.5 lux, and, to avoid glare, the illumi- nation in region B should be less than 0.7 lux. The illumination at point 50 V should be greater than 3 lux. There should be a clear cut-off line below the H-H plane of 250 mm. C. Candle Power Distribution Curve A candle power distribution curve shows the normalized inten- sity of a light source at each degree of the chip emitting surface as shown in Fig. 3. The normal direction is at 0 deg, and the radial direction is the normalized intensity. The optical effi- ciency can be calculated by analyzing the candle power distri- bution curve. The angular distribution of the light emission of Fig. 3. the white LED is from −90° to 90°. The yellow region is the Optical efficiency is 78.48%, and the light distribution of the white LED is from −60° to 60°. design region having a light distribution from −60° to 60°, so the optical efficiency of the design requirement is more than 78.48%. 3. MOTORCYCLE HEADLAMP DESIGN D. Average Deviation A. Spread Angles of the Light Source Projected onto The average deviation is calculated from the ratio of the stan- the Measuring Screen dard deviation to the average as given by Eq. (1). By computing The distance from the headlamp to the measuring screen the average deviation for the entire measuring screen, we could is 25 m. The size of the measuring screen is 4500 mm × completely determine the uniformity of the light pattern on the 1000 mm. The relationship of the spread angle of the light measuring screen. The smaller the average deviation, the better source on the measuring screen is shown in Fig. 4. The spread the uniformity: angle is 10.28° in the horizontal direction and 2.29° in the qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiP 1 N X − X 2 vertical direction, indicating the angles of the light source σ N i1 i ; (1) projected on the measuring screen. Average Deviation X X B. Luminous Flux Calculation X σ N where is the average, is the standard deviation, and is the It is difficult to design the high beam for an irregular illumi- number of sampling points. nation distribution, as shown in Fig. 1. The maximum illumi- nation requirement is 12 lux. In order to simplify the design, consider the high beam illuminating a measuring screen of 4500 mm × 1000 mm to be 12 lux. The total luminous flux is 54 lm. The height is defined by the size of the motorcycle; we set the height of the motorcycle headlamp (HV) to be 750 mm from the road. The design calls for the headlamp to be 25 m from the measuring screen. The height of 1000 mm of projected illumination is 750 mm in the vertical direction over the road and 250 mm below, as shown in Fig. 5. The vertical angle of the high beam is 2.29°, and the minimum distance irradiating the road is 18.76 m. Fig. 1. Illumination requirements for a high beam projected onto a The illumination requirements for the low beam are shown measuring screen in order to meet ECE R113. in Fig. 2. The maximum illumination of the low beam on the E104 Vol. 54, No. 28 / October 1 2015 / Applied Optics Research Article Fig. 7. Picture of the Osram LW-W5SN LED. Fig. 4. Spread angle of the light source projected onto the measur- ing screen. Fig. 5. Lateral view of the high-beam irradiation on the road. Fig. 8. Light distribution curve of Osram LW-W5SN LED. measuring screen is 3 lux in an area 4500 mm × 1000 mm. The total luminous flux needed is 13.5 lm. For the low-beam design, the angle of the high beam is rotated 0.86° downward to lighting would preferably be more than 20 lux.