1 Introduction

During the “Eleventh Five-Year Plan” period, China is committed to transforming China from the current inefficient energy users into efficient energy users – the energy consumption per unit of GDP is reduced by about 20%, and governments and departments at all levels also build resources. A conservation-oriented and environment-friendly society is an important part of the development of the 11th Five-Year Plan. In China's power energy consumption, lighting electricity accounts for about 13% of total energy consumption. The National Development and Reform Commission clearly stipulates that lighting energy saving is an important part of China's energy conservation in the “Eleventh Five-Year Energy Conservation Plan”, improving the quality of lighting and Level, reduce light pollution, establish a high-quality, efficient, economical, comfortable, safe and environmentally friendly lighting system, which is an important strategic measure to ensure the sustainable development of China's energy, and the search for new, efficient, energy-saving, high-quality environmental protection is a problem. The key [1 ~ 2].

As a new type of light source, LED (Light Emitting Diodes) is considered to be the most energy-saving product in the 21st century, and has attracted worldwide attention to its application in the field of energy conservation. The existing LED products are mainly used in decoration, landscape, signal, red and green traffic lights, garden lights, car lights and some special-purpose lighting fields. Companies such as GE, Germany, SIEMENS, OSRAM, and Japan's SONY are also working on next-generation application development for LED lighting products and lighting systems. In 2006, China officially launched the “National Semiconductor Lighting Project”, which has initially formed four major LED lighting R&D areas in the Pearl River Delta, Yangtze River Delta, Jiangxi, Fujian, Beijing and Dalian [3 - 4]. With the continuous breakthrough of LED technology, LED will have a broader application prospect. Based on the characteristics of LED light source, this paper mainly introduces the demand advantages of LED for tunnel lighting and some existing problems, and hopes to bring some enlightening ideas to tunnel construction engineers.

2 LED requirements for tunnel lighting

With the rapid development of China's economy and transportation, the number of road tunnel construction is increasing. Due to the special environment inside the tunnel, in order to ensure the safety of the driver's driving, according to the national tunnel lighting design standards, tunnels with a length of more than 100 meters should be equipped with lighting facilities. But not all lighting sources are suitable for tunnel lighting, and the reasonable choice of light source and luminaire is the key to ensure the quality of tunnel lighting. In addition to the main requirements for light efficiency, life, color, color temperature, light distribution, heat dissipation, and maintenance in tunnel-specific environments, the source of tunnel illumination should also be satisfactory in the formation of smoke from exhaust emissions from automobiles. The requirements of visibility, tunnel lighting effects must rely on reliable light sources to achieve. At present, most of the tunnel lighting in China uses incandescent lamps, fluorescent lamps, high-pressure sodium lamps, low-pressure sodium lamps, etc. Most of them have problems such as narrow optical band, insufficient light distribution quality, high energy consumption, poor quality stability, short life, and low grade [5]. And the lighting control method is backward, resulting in poor tunnel lighting effect, unable to meet the driving requirements, seriously affecting the driving safety, and at the same time making the tunnel lighting operation and maintenance costs remain high, resulting in great waste of energy.

The research results of Ming Vision and intermediate vision theory, color rendering and illuminance show that [6], LED has inherent advantages in tunnel lighting, compared with traditional lighting source, it has long life, easy control, high efficiency and color rendering. High performance, controllable color temperature range, etc. If combined with the optimized design of optical, electrical and thermal aspects, it can greatly improve the current level of tunnel lighting in China, save energy and maintain the sustainable development of tunnel construction.

3 LED tunnel light classification and light source characteristics

3. 1 LED Tunnel Light Classification

Currently, LED tunnel lights in the market can be classified according to shape, light source, structure, and luminous intensity and operating current. 1) Classification by shape: There are two types of circular products and rectangular products (Fig. 1, Fig. 2). The rectangular products can be divided into two types: flat shape and trapezoidal according to chip arrangement. Since the tunnel is rectangular, it is required to illuminate the road surface and the height of the tunnel wall by 2m. When the light source design of the light source reaches the same level, the circular product must meet the brightness standard specified by the specification, and the necessary lamps are necessary and the uniformity is poor. And rectangular products are easier to meet the requirements of the specification.

2) Classification by light source: According to chip power, it can be divided into high-power LED tunnel light and low-power LED tunnel light. The advantages of Japanese and American famous brand chips in terms of stability and light decay have been recognized by the industry. As for the comparison between high-power LED tunnel lights and low-power LED tunnel lights, it is related to the heat dissipation performance and actual power consumption of the products.

3) Classified by structure: Integrated structure, modular structure

Three forms with semi-modular structures. The integrated structure tunnel lighting combines the light source, the lamp and the power supply into one, which is inconvenient to maintain; the modular structure separates the light source, the lamp and the power supply, and the chip or power supply in the light source is faulty, and can be replaced and convenient for maintenance. The semi-modular structure separates the power supply from the light source and the luminaire, facilitating power supply replacement, regardless of chip failure.

4) According to the luminous intensity and working current classification: LED with ordinary brightness (luminous intensity less than 10cd); ultra-high brightness LED (luminous intensity greater than 100cd); high-brightness LED with luminous intensity between 10 and 100cd. The operating current of a typical LED is between ten mA and tens of mA, while the operating current of a low current LED is below 2 mA.