Design and Prototyping of Efficient LED Counter Beam Light with Free-Formed Surface for Meeting International Tunnel Lighting Standards

Abstract

An LED Counter Beam Light (CBL) with a free surface secondary lens is proposed to enhance the safety and efficiency of tunnels. The secondary lens was designed and produced to be mounted on a 50 W white-light LED array to generate the targeted counter beam pattern, in order to meet the standards for enhanced tunnel road lighting of the CIE (Commission Internationale de l’Eclairage)—CIE 88:2004—in a trial tunnel lighting scheme. Through the simulation of a road tunnel in Northern Taiwan using the LiteStar four-dimensional software, it was shown that the proposed LED light can serve as a qualifying CBL to generate an average road tunnel surface luminance (Lav) of 182.76 cd/m2, which is better than the 138 cd/m2 that commercial High-Pressure Sodium (HPS) tunnel lights can provide and the 181 cd/m2 minimum stipulated in the CIE 88:2004 regulations. The results also show that the proposed LED light accomplishes a contrast revealing coefficient qc of 1.03, which is above the minimum regulatory level of 0.6 for a qualified CBL, as well as a luminance uniformity Uo of 0.89 (regulatory minimum, 0.4), longitudinal luminance uniformity UL of 0.99 (regulatory minimum, 0.6), and glare factor TI (threshold increment) of 7.24% (regulatory minimum, 15%). In order to test the feasibility of the LED CBL for future commercialization, the proposed LED CBL was prototyped and measured; the results demonstrate that an average road surface luminance (Lav) of 184.5 cd/m2, intensity of the luminance uniformity Uo of 0.7, intensity of the longitudinal luminance uniformity UL of 0.94, glare factor of 7.04%, and contrast revealing coefficient qc of 1.38 can be achieved, which are all above the levels required by the CIE 88:2004 regulations.