LED (LightEmittingDiode) light-emitting diode, is a way to convert electrical energy into visible light solid-state semiconductor devices. LED light-emitting principle is the current through the compound semiconductor, through a combination of electrons and holes, in the form of excess energy will be the release of light, to achieve the effect of light.
Since the birth of the first commercial LED 1960, LED light source is obtained rapid development and application. Originally used as a multi-LED lights, display panels, with white LED appeared, and their use has been greatly improved, now in traffic signals, advertising signs, emergency lighting, LCD backlighting, automotive lighting, commercial lighting as well as many other areas of the city at night lighting landscape lighting engineering has been widely used. Therefore, LED light source is known as fourth-generation light source or green light, in the 21st century a new generation of light source.
In recent years, with the further implementation of the rapid development of LED lighting technology and energy saving policies, LED light source has been used in street lighting and road tunnel lighting. According to statistics, China's development and production of white LED light source for road and tunnel lighting companies have hundreds. Using LED as a light source of the tunnel is gradually increasing, such as Shanghai Yangtze River Tunnel, Beijing Desheng mouth tunnels. Any new thing must have a development and improvement process, therefore, be applied at the beginning of the tunnel lighting LED light source, we should as soon as possible knowledge and understanding of LED light source advantages and disadvantages in the current tunnel lighting, give full play to the advantages of the LED light source, a front existing problems. We thus provide a reference for the correct use of LED light in the tunnel lighting, LED light source for the future in the tunnel lighting application and development direction.
1, features LED light source
LED light source as a new generation of light, incandescent, high pressure sodium and other traditional thermal radiation and gas discharge light sources, compared with a very different, the current LED light source has the following advantages in lighting:
(1) Small
LED light source, compared to traditional light sources, small size, light weight, can be made into various shapes of devices, ease of layout and design of various fixtures and equipment, adaptable for a wide range.
(2) environmental performance
Since the LED light source in the production process without the addition of metallic mercury, and therefore discarded after LED will not cause mercury pollution, and it is almost all the recycling of waste, not only saves resources, but also protect the environment.
(3) Security and Stability
LED light source can be driven by low voltage DC, usually supply voltage between 6 ~ 24V, so the safety performance is better, especially for public places. Also in the good external environment condition, LED light source than traditional light decay, long life, even frequent switching, it does not affect their life.
(4) seismic, impact resistance
The basic structure of the LED light source is an electroluminescent semiconductor materials, placed on a wire rack, then sealed with epoxy resin around, no glass in the structure of the shell, do not like the incandescent or fluorescent lamps as in within evacuated or into a specific gas. Therefore, LED light source of the earthquake, good impact resistance, to their production, transportation, use various links to bring the convenience.
(5) strong directivity
Compared with traditional light source, light emitted from the LED light source is directional, most of the light emitted from the LED is face to face directly toward the utilization rate is much higher than conventional light sources.
(6) fast response time
Response time incandescent millisecond response time of the LED light source, compared with nanosecond. Therefore, widely used in traffic signal lights and automotive fields.
(7) high luminous efficiency
With the development of LED lighting technology, the luminous efficiency of the LED light source has increased from less than 10lm / W up to 100lm / W or more, and the luminous efficiency is still a large potential for improvement.
(8) Light color rich
LED light source by changing the current, chemical modification, monochromatic light mixing method, various colors can achieve visible light emitting and discoloration, even for the white LED may also be made into a variety of color temperature of the light source. Therefore, in the interior lighting and landscape lighting has obvious
Advantage.
(9) no flicker, no UV
LED light source uses a DC power supply, light stability is not blinking, and the spectrum mainly in the visible region, almost no interference of ultraviolet or infrared radiation, thus avoiding the adverse effects of stroboscopic effect caused by increasing human eye comfort.
(10) with adjustable brightness and good
The light emitting principle LED light source, LED brightness or luminous flux output substantially with the current positive changes. The operating current within ratings vary, with good adjustability, on-demand illumination LED light source, the brightness stepless control of the foundation.
It is because LED light source with more traditional light sources can not match advantage, the LED light source become the focus and direction of the development of lighting States.
2, the characteristics of the light source and tunnel lighting requirements
Tunnel lighting is to ensure the smooth flow of traffic in the tunnel and set up functional lighting, lighting its purpose is to give the driver to provide a safe and comfortable visual environment in the tunnel driving, traffic operations to protect and improve transport efficiency. Since the tunnel is a semi-enclosed space, the visual characteristics of a tunnel on the road than other lighting is much more complicated, it requires not only 24h continuous lighting, and lighting during the day than at night the lighting is more complex. Thus, tunnel lighting has the following features:
(1) segmented lighting
Segmented lighting tunnel lighting is the most significant features. This is because during the day inside the tunnel and the light path of the external environment has undergone great changes, visual need some time to adapt to the situation to see the road. Therefore, in order to allow the driver ends of the tunnel entrance to have a good visual transition, tunnel lighting is divided into several different lighting segments: inlet section, a transition section, an intermediate section and an outlet section, and each lighting segment surface brightness level different requirements, as shown in FIG. Wherein the inlet section, surface brightness level of the transition period is necessary to determine based on the brightness of the tunnel outside the cave.
(2) enhance the lighting
Since the tunnel during the day and night lighting requirements are different, so the lighting inlet section, transition section and the outlet section is substantially strengthened by the basic lighting and lighting of two parts, according to the former middle section consider lighting, which can be used to strengthen the power of large lamps illumination. Meanwhile, emergency lighting and parking zone at the connecting passage has a corresponding lighting requirements.
(3) Avoid / smoke effect
Due to limitations of ventilation inside the tunnel, car exhausts easy rapid dilution, prone to gather the formation of smog, thereby generating / smoke effect 0. Thus, in the tunnel lighting design and source selection must take into account their impact.
It is because of tunnel lighting has characteristics as described above, the current industry standard of 5 highway tunnel ventilation lighting design 6 pairs of tunnel lighting and lamps made the following requirements:
(1) In general should choose high efficiency, good performance through the fog light source;
(2) short tunnel, fewer diesel vehicles near the town of tunnels, emergency parking zone, pedestrian cross-channel, cross-channel car dealers can choose a higher CRI light source;
(3) the life of the light source should not be less than 10000h;
(4) lamps and lanterns protection grade not lower than IP65;
(5) should have the anti-glare lighting apparatus for highway tunnel characteristics;
(6) lamp structure should be easy to replace the lamp and accessories;
(7) lighting components should have good corrosion resistance;
(8) Fixtures for the installation should be easy to operate, and can adjust the angle;
(9) lamps must not invade tunnel construction boundaries;
Lighting arrangement (10) in the middle section should meet less than 2.5Hz or higher than 15Hz flicker frequency.
3, LED light source opportunities and challenges in the tunnel lighting
With the rapid development and promote the popularity of LED lighting technology, LED light source used in the tunnel lighting is gradually increasing, LED light source because of its small size, good environmental performance, security and stability, high luminous efficiency, adjustability and good in the tunnel lighting has good prospects and opportunities.
(1) have good optical properties
On the luminous efficiency, although at this stage LED Tunnel Light is not the most efficient light-emitting light source, compared with fluorescent and metal halide or have certain advantages; In addition, since the LED light source directivity, small volume, while the LED package optical design can be carried out through scientific and rational design of secondary optics, LED tunnel lights can achieve higher than high-pressure sodium lamps tunnel effective luminous efficiency.
In life, although in practice, due to the influence of other aspects of packaging technology, LED light source is difficult to achieve more than 100000h theory of life, but the actual life 20000h still around at this stage, and still meet the requirements of tunnel lighting of the light source , it has a high service life.
In the light source color, white LED light source can reach more than 80 color rendering index, used in tunnel lighting can make the driver have better clarity and visibility, significantly improve the ability to identify and reaction speed to avoid accidents. At the same time, the color temperature of white LED light source can also be customized, thus facilitating research tunnel lighting visual effect of different color temperature light source, choose more suitable for tunnel lighting color temperature of the light source.
(2) help to improve the quality of tunnel lighting
For most conventional light sources, the general high power light source is often its high luminous efficiency, luminous flux. Therefore, when road lighting, to ensure uniformity road illumination of the premise, generally choose the larger power source, which can improve efficiency, increase the spacing between luminaires, reducing the number of poles and lamps, and reduce costs. For tunnel lighting, though without the installation of additional lighting poles, but due to the relatively low efficiency of conventional low-power light source, and the need to increase the number of lamps, therefore, as far as possible power source selection.
As for the LED light source, although used in tunnel lighting, high-power LED light source, but the power of a single light source is generally between 1W ~ 3W, which is composed of a plurality of tunnel light power LED light source through series and parallel combinations into therefore, LED tunnel lights can be combined as desired, to reduce the power of a single tunnel lights, shorten the distance between the lamps, bringing some of the following benefits:
1) Avoid glare
Because of the reduced single tunnel lamp power, the brightness is reduced, thus avoiding driving the process, especially in backlit glare interference since the light source is too bright lighting conditions produced.
2) improve the brightness uniformity
Since the distance between the lamps shorter, less prone to lighting between / 0 dark areas, and with a good secondary optical design, it can greatly improve road tunnel brightness uniformity and target visibility.
3) Avoid stroboscopic effect
Stroboscopic effect (flickereffect) is a phenomenon when driving through cyclical changes in lighting and shade produced. Flashing frequency (ie, stroboscopic effect) f = v / s (where v is the speed, s is the distance between the lamps) should meet less than 2.5Hz or higher than 15Hz requirements. Therefore, the distance between the lamp easy to make a short flicker frequency higher than 15Hz, more uniform brightness distribution of the light source but also conducive to weaken the stroboscopic effect brought about by the uncomfortable phenomenon.
4) enhanced visual guidance
Due to the short distance between the lamps, arranged in order, and LED tunnel lighting has a certain lightness, relatively easy to form a bright band of light to alert the driver to pay attention to changes in the direction of the road, so that the tunnel has a good visual guidance, as Fig.
As can be seen from the above, LED tunnel lights through scientific design and layout, especially the use of LED light ribbon or strip lighting, it can greatly improve the quality of tunnel lighting.
(3) in favor of intelligent tunnel lighting stepless control
In the tunnel lighting standards set forth, should be rated adjust lighting levels inlet section, transition section and an outlet section according to the brightness outside the cave and traffic changes. The traditional tunnel light (high pressure sodium and metal halide lamps) mainly by the closure of some light sources to achieve dimming requirements, in this way on the one hand will increase the number of lamps and lighting circuits, on the other hand will reduce the quality of tunnel lighting, prone / 0 zebra effect.
The LED light source due to good brightness adjustable, so you can achieve on-demand lighting, brightness stepless control. Promise dimming performance LED tunnel lights is one of its greatest strengths and highlights, if the combination of intelligent lighting control systems, intelligent control stepless tunnel lighting, the lighting of the cave during the day can enhance the actual luminance variation according to the tunnel outside the cave real-time adjustment control, synchronization midnight adjusted according to changes in the basic traffic tunnel illumination, and does not produce / 0 zebra effect, avoid excessive lighting, to meet the safety and comfort of the premise of the maximum energy saving lighting.
(4) easy installation and maintenance
LED tunnel lights by a plurality of LED light source is assembled into modules assembled together, modular installation to install, no extra wiring, easy to install.
LED tunnel lights also superior to conventional sources of light in the tunnel maintenance. Traditional light tunnel lamp reaches the lifetime of the lamp must be replaced, and LED tunnel lights thanks to the modular, once the light goes out individual phenomenon, just replace one of the modules without causing the lamp appears can not be used from this point of view, LED tunnel lights save energy advantages also exist. Meanwhile, the long-life LED light source, which means that without frequent replacement, thereby reducing the potential for traffic disruption, reducing the maintenance costs for this payment.
Although the LED light than traditional light sources more some of the above advantages, and tunnel lighting is to promote, but the LED light source in the popularization and application of tunnel lighting still faces the following challenges in the tunnel lighting
(1) high price
The high price of LED application unavoidable problem, especially at higher price High Power LED light source. A 100W LED tunnel lamp with a 150W high-pressure sodium lamp efficacy similar, but the price of a high-150W high pressure sodium lighting equipment about 800 yuan, while the price of a set of high-quality lighting 100WLED about 4,000 yuan, the price difference 5 times. Therefore, an important reason for the larger one-time investment and cost-effective products is the impact of the current popularity of LED tunnel lighting.
(2) cooling problems
High pressure sodium, metal halide arc tube and other traditional sources of work are needed to maintain a high outer bulb wall temperature, sealed lighting source for this work it is beneficial. However, this LED light source is very harmful, because there will be 70% LED work even higher proportion of energy converted to heat radiation can not rely on the release, and poor ventilation inside the tunnel, the temperature can easily rise. The LED semiconductor light emitting device as its own temperature will change its characteristics will be significant changes, especially the PN junction temperature rise will lead all aspects of device performance variation and attenuation. This change is mainly reflected in three aspects:
1) to reduce the external quantum efficiency of the LED;
2) shorten the life of the LED;
3) causing the light emitted from the LED main wavelength shift, resulting in color of the light shifted.
Therefore, the heat source is an important challenge in LED tunnel lighting faced, otherwise it will greatly affect the normal operation of the LED, reduce the luminous efficiency, the light fades to accelerate and shorten life.
In addition to these two major bottlenecks limiting the development of LED tunnel lighting, the current LED light source efficiency, packaging technology and materials, the driving circuit, the second optical design, product and testing standards and other outstanding issues related to mature and improve, these issues are LED light source will be the challenge in the next tunnel lighting and other lighting application in the face.
4. Conclusion and Outlook
LED light source as a new generation of light source, with high efficiency, energy saving, environmental protection, etc. by national and local government support and promotion. Its applications have gradually by the signal indication, emergency lighting and other small power lighting extended to roads and road lighting tunnel lighting and other high-power lighting. In the tunnel lighting, LED light source in addition to having good optical properties, but also has to improve the quality of tunnel lighting, intelligent stepless control and easy ongoing maintenance and other advantages, which brought well as LED light source in the lighting of the tunnel opportunity. At the same time, LED light source in the current tunnel lighting still face high prices and difficult to heat two major challenges, as well as LED lighting technology is not yet mature challenge.
Thus, in the current tunnel lighting should be avoided exaggerating the effect of LED light source, quick success, the blind use, LED light source in the tunnel lighting remains to further research and testing, and to establish standards for LED tunnel lighting design, management and operating system, standardization of LED lighting products, LED light source really play the advantages of tunnel lighting. At the same time, we should also see LED lighting technology development momentum and broad prospects in addressing the current problems facing the rear, LED light is the tunnel that even according to the direction of other lighting development.
