Review of optical design for vehicle forward lighting based on white LEDs

Ching-Cherng Sun,Shih-Kang Lin,Yi-Jou Lin,Cheng-Yan Hsieh,Yeh-Wei Yu,Yong-Sheng Lin,Tsung-Hsun Yang,Chi-Shou Wu

doi:10.1117/1.oe.60.9.091501

Abstract

We introduce a current development in optical design for vehicle forward lighting based on solid-state lighting, in particular, phosphor-converted white LEDs. The vehicles include bicycles, bikes, and automobiles. Although the requirements regulating different vehicles are different, the low beam always requires a high-contrast cutoff line. Three optical design approaches are discussed; these include a projection lens incorporated with a baffle or beam shaper, multisegment reflectors, and complex lenses. A new design approach called light field management technology for the multisegment reflector is introduced. In addition, the possible related manufacturing errors and the robustness of different optical approaches are analyzed. Finally, we introduce three approaches to adaptive forward lighting that provide a driver with brighter and clearer vision without inducing glare to people on the roadway. The application of video projection technology to roadway illumination could be a trend of vehicle forward lighting based on solid-state lighting.

Highlights

A white LED is made with a blue die covered with yellow phosphor to perform downconversion, so it is called a phosphor-converted white LED.[1,2,3,4,5,6,7,8,9,10] PcW-LEDs have been extensively applied to general lighting and special lighting
We focus on the study of the optical design of forward lighting excluding the daytime running light
Different from the regulation for an automobile, the light pattern of the low beam for a bike is symmetrical along the horizontal direction, but the cutoff line is required to provide high linearity and high contrast

Summary

Introduction

A white LED is made with a blue die covered with yellow phosphor to perform downconversion, so it is called a phosphor-converted white LED (simplified pcW-LED).[1,2,3,4,5,6,7,8,9,10] PcW-LEDs have been extensively applied to general lighting and special lighting. Even with a luminous efficacy below 100 lm∕W, in 2007, the world’s first LED headlamp was equipped in a luxury car,[15] and this was the starting point of a new era of LED for automotive forward lighting It means that the optical properties of pcW-LEDs met the requirements of a headlamp owing to their advantages in luminous efficiency and exitance. Different from the regulation for an automobile, the light pattern of the low beam for a bike is symmetrical along the horizontal direction, but the cutoff line is required to provide high linearity and high contrast. The light pattern of the high beam is spread horizontally with less brightness required in comparison with the regulation for an automobile. A bicycle headlamp cannot consume too much electrical power, and the price must be low; the design for a bicycle headlamp is as complicated as that in the other vehicles

Characteristics of pcW-LEDs

Optical Design Approaches

Adaptive Headlamps

Summary