Glare Effect for Three Types of Street Lamps Based on White LEDs Ching-Cherng SUN  , Chong-Jhih JIANG, Yi-Chun CHEN, and Tsung-Hsun YANG Department of Optics and Photonics, Institute of Lighting and Display Science, National Central University, Chungli 320, Taiwan (Received October 9, 2013; Accepted February 18, 2014) This study is aimed to assess the glare effect from LED-based street lamps with three general optical designs, which are cluster LEDs with a single lens, a LED array accompany with a lens array, and a tilted LED array, respectively. Observation conditions were simulated based on various locations and viewing axes. Equivalent luminance calculations were used to reveal the glare levels of the three designs. The age effect for the calculated equivalent luminance was also examined for human eyes of people at the age of 40 or 60. The results demonstrate that among the three design types, a LED array accompany with a lens array causes relatively smaller glare for most viewing conditions. # 2014 The Japan Society of Applied Physics Keywords: LED-based street lamps, LED arrays, direct luminance, veiling luminance 1. Introduction The advantages including high efficiency, free of mercury, energy savings, and compact sizes for easy light shaping, have led white light emitting diode (LED) to become a modern new light source for general lighting, including street lighting. 1–4) However, stronger glare effects may also be introduced due to the compact size. Especially the high luminance could be observed from the white-LED based street lamps. To prevent traffic accidents caused by the visual disturbances, it is important to address the glare effect of outdoor lighting, especially the street lamps. 5,6) The Standard Practice for Roadway Lighting recommended by American National Standards Institute and IES provides a way to restrict the glare effect from street lamps. 7) It suggests controlling the ratio of veiling luminance to average background luminance below 0.3 for main roads and 0.4 for secondary roads, respectively. 7) The concept of the restriction is to prevent the higher veiling luminance from reducing the image contrast in driver’s visual field. 8,9) Note that the veiling luminance is from the stray light detected by fovea due to the ocular scatter. 10,11) Another recommendation from CIE (No. 155-1995) suggests two parameters which are threshold (TL) and discomfort glare (G) to assess the glare effect. 12) TL is determined by the ratio of veiling luminance to average background lumi- nance and G is determined by the intensity of street lamp in certain large viewing angle. The viewing angle here is defined as the angle between the normal vector of the lamp and the line through the eye and the lamp. It reveals the suggestion of glare prevention from CIE, which considers not only veiling luminance but also the direct intensity in the large angles between 80 and 88  for discomfort glare. In the condition of large viewing angles, the driver would get more probability to see the lamp directly. Additionally, the emitting area is ignored here because of the far observation position, and therefore the intensity replaces the luminance. According to the glare prevention mentioned above, the two important factors are concluded as the veiling luminance and direct luminance if the emitting area is considered. Note that the veiling luminance is the visual behavior of disability glare and the direct luminance is the main parameter in discomfort glare. 13) In consideration of the IES and CIE recommendations for glare, this study is aimed to assess the glare level for three different street lamps based on white LEDs. Optical designs of street lighting are summarized as three major types to represent the general cases, including cluster LEDs with a single lens (simplified as CSL), a LED array accompany with a lens array (simplified as ALA), and a tilted LED array (simplified as TA), 14–18) as illustrated in Fig. 1. All these popular designs can achieve requested uniformity and illuminance on roadway and have been practically operated in roadway lighting in the past few years. 2. Calculation and Simulation 2.1 Geometry of the defined light source Each light source is first described as a matrix for numerical computations. Figure 2 shows an emitting surface model that the area of white LEDs is regarded as a matrix, where each light source unit is 5 cm apart from each other. The matrix size here is a variable but the lamp still has a fixed total output flux and a fixed lighting pattern. The (a) (b) (c) Fig. 1. (Color online) The three major types of optical design for LED street lamps: (a) CSL type, (b) ALA type, and (c) TA type.  E-mail address: ccsun@dop.ncu.edu.tw OPTICAL REVIEW Vol. 21, No. 3 (2014) 215–219 215