0 Preface
LED (Light Emitting Diode) is a solid-state semiconductor device capable of converting electrical energy into visible light. The principle of LED illumination is to pass current through the compound semiconductor. Through the combination of electrons and holes, the excess energy will be released in the form of light to achieve the effect of luminescence.
Since the birth of the first commercial LED in the 1960s, LED light sources have been rapidly developed and applied. LEDs are mostly used as indicators, display panels, etc. With the advent of white LEDs, their application range has been greatly improved. Now in traffic signals, advertising signs, emergency lighting, LCD backlighting, automotive lighting systems, commercial lighting And a wide range of applications in many lighting fields, such as urban nightscape lighting projects. Therefore, the LED light source is called the fourth-generation illumination source or the green light source, and has become a new generation of light source in the 21st century.
In recent years, with the rapid development of LED lighting technology and the in-depth implementation of China's energy saving and emission reduction policies, LED light sources have also begun to be applied to road lighting and road tunnel lighting. According to statistics, there are already hundreds of road and tunnel lighting companies that develop and produce white LEDs as light sources. Tunnels using LEDs as illumination sources have also gradually increased, such as the Haichangjiang Tunnel and the Beijing Deshengkou Tunnel. Any new thing must have a process of development and improvement. Therefore, in the initial stage of LED lighting application, we should understand and understand the advantages and disadvantages of LED light source in current tunnel lighting as soon as possible, and give full play to the advantages of LED light source. The shortcomings of existence. This provides a reference for the correct use of LED light sources in tunnel lighting, and provides a direction for the future application and development of LED light sources in tunnel lighting.
1 LED light source features
LED light source as a new generation of light source, compared with traditional thermal radiation and gas discharge light sources such as incandescent lamps and high pressure sodium lamps, the current LED light source has the following advantages in lighting:
(1) small size
Compared with the traditional light source, the LED light source is small in size and light in weight, and can be fabricated into various shapes of devices, which is convenient for arrangement and design of various lamps and equipments, has strong adaptability and wide application range.
(2) Good environmental performance
Since the LED light source does not need to add metallic mercury during the production process, the LED will not cause mercury pollution after being discarded, and the waste can be almost completely recycled, which not only saves resources but also protects the environment.
(3) Safe and stable
The LED light source can be driven by low-voltage direct current. The general supply voltage is between 6 ~ 24 V, so the safety performance is better, especially suitable for public places. In addition, under the favorable external environment, the LED light source has less light decay and longer life than the conventional light source, and even if it is frequently switched, it does not affect its service life.
(4) Good earthquake resistance and impact resistance
The basic structure of the LED light source is an electroluminescent semiconductor material placed on a leaded shelf and then sealed with epoxy resin. There is no glass casing in the structure, and it does not need to be inside the lamp like incandescent or fluorescent lamps. Drain or rush into a specific gas. Therefore, the LED light source has good seismic and impact resistance, which brings convenience to its production, transportation and use.
(5) strong directivity
Compared with the traditional light source, the light emitted by the LED light source is oriented, and most of the light emitted from the LED can be directly directed to the illuminated surface, and the utilization rate is much higher than that of the conventional light source.
(6) Fast response time
The incandescent lamp has a response time of milliseconds and the LED light source has a response time of nanoseconds. Therefore, it is widely used in the field of traffic signals and car signal lights.
(7) High luminous efficiency
With the development of LED lighting technology, the luminous efficiency of LED light sources has increased from less than 10 lm/W to more than 100 lm /W, and its luminous efficiency still has a great potential for improvement.
(8) rich in light color
The LED light source can realize light emission and discoloration of various colors in the visible light band by changing current, chemical modification, monochromatic light mixing, etc. Even for white light LEDs, light sources of various color temperatures can be produced. Therefore, it has obvious advantages in interior lighting and landscape lighting.
(9) No flicker, no UV
The LED light source adopts DC power supply, the light is stable and does not flicker, and the spectrum is mainly concentrated in the visible light region, and there is basically no interference of ultraviolet rays or infrared radiation, thereby avoiding the adverse effects caused by the stroboscopic effect and improving the comfort of the human eye.
(10) Brightness is adjustable
According to the principle of illumination of the LED light source, the luminance or output luminous flux of the LED changes substantially with the current. The working current can be large or small within the rated range, and has good adjustability, which lays a foundation for the LED light source to achieve on-demand illumination and brightness stepless control.
It is precisely because LED light source has the advantage that the above traditional light source can't match, LED light source has become the focus and direction of the development of lighting industry in various countries.
2 Characteristics of tunnel lighting and requirements for light source
Tunnel lighting is a functional lighting designed to ensure smooth traffic in the tunnel. The purpose of the lighting is to provide the driver with a safe and comfortable visual environment during the tunnel driving, to ensure traffic operation and improve transportation efficiency. Since the tunnel is a semi-enclosed space, the tunnel is much more complicated in terms of driving visual characteristics than other lighting. It requires not only 24 hours of uninterrupted lighting, but also daytime lighting is more complicated than night lighting. Therefore, tunnel lighting has the following characteristics:
(1) Segmented lighting
Segmented lighting is the most prominent feature of tunnel lighting. This is because the light environment inside and outside the tunnel has changed a lot during the daytime, and the vision needs a certain adaptation time to see the road. Therefore, in order to allow the driver to have a good visual transition at the entrance and exit of the tunnel, the tunnel illumination is divided into several different lighting segments: the entrance section, the transition section, the intermediate section and the exit section, and each illumination section The road surface brightness level requirements are different, as shown in Figure 1. The road surface brightness level of the entrance section and the transition section needs to be determined according to the brightness outside the tunnel hole.
