With the rapid development of China's economy, people's requirements for road lighting quality are getting higher and higher. Highway tunnels have the characteristics of shortening mileage and using underground space. Motor vehicle drivers visually feel the brightness of the road surface when driving, especially the difference in brightness inside and outside the tunnel has a great impact on traffic safety. In order to coordinate the management of traffic safety and energy saving, the dimming control of lighting lamps by the tunnel management center is still important.

Jiang Shuping, chairman of the Tunnel Engineering Branch of the China Highway Society, mentioned in the 2016 National Highway Tunnel Academic Annual Conference report that my country's highway tunnels have been completed to 12683.9km, a year-on-year increase of 15.2, ranking first in the world. How to improve the safety and comfort of highway tunnel lighting and reduce operating costs has become the focus of attention of relevant departments. It is urgent to adopt high-efficiency energy-saving technology to reduce energy consumption and realize "on-demand lighting". In order to better improve lighting quality and ensure driving safety and comfort, LED(light emitting diode,LED) with high efficiency, energy saving and easier control has been widely promoted and applied in lighting, the combination of LED and intelligent control technology will realize the efficiency improvement of "intelligent change due to demand and energy saving upgrade.

1. tunnel lighting system:

1.1 system construction:

china's transportation road network is extending in all directions, and the comfort of driving has attracted more and more attention. How to make the driver more comfortable when passing through the tunnel from bright to dark and then to bright is the best interpretation of the lighting designer's design of the tunnel lighting scheme. The tunnel lighting control system is networked by the control center with one or more groups of programmable controllers of LAN points. The unit programmable controller controls the regulation of the group of tunnel lighting lamps. The environmental information detector of the system collects the environmental information inside and outside the tunnel and the information of passing vehicles. The optical fiber network is used to transmit the corresponding information to the control center server for processing, and then the dimming instruction is transmitted to the LED tunnel lamps in each section of the tunnel for dimming control.

In order to ensure that the brightness after the dimming command is executed can reach the required value, when the real-time detection of the illumination in the tunnel cannot meet the lighting requirements, the control center performs dimming processing according to the detection information, so that the lighting brightness can meet the tunnel lighting quality requirements to ensure The driving safety of the vehicle.

1.2 system design guidelines:

highway tunnels are mainly divided into urban tunnels, mountain tunnels and underwater tunnels. due to the particularity of China's geographical conditions, tunnel construction is difficult, and due to the mutual interference of two-way traffic lights, most tunnels adopt one-way traffic design scheme. Generally, the lighting requirements and quality of the tunnel entrance section, transition section, middle section and exit section are not the same. During the day, the illuminance decreases step by step from the tunnel entrance to the middle section, and the illuminance from the middle section to the exit section increases step by step.

With people's high attention to "permeability" and "intermediate vision", as well as the application of new technologies such as LED, intelligent control and wireless transmission, tunnel lighting quality will become more comfortable and energy-saving. Tunnel lighting should be designed in combination with highway grade, tunnel length, design speed, traffic volume and local weather and other conditions, and should conform to the the People's Republic of China Ministry of Transport (Ministry of Transport of the People's Republic of China,MOT) issued by the industry standard JTG/T D70/2-01-2014 "Highway Tunnel Lighting Design Rules" corresponding requirements.

1.3 "LED + Smart" control:

tunnel lighting mostly adopts timing control method, and the control purpose is achieved by controlling the number of lighting lamps in different circuits. The "LED + intelligent" lighting system with innovative technology application consists of programmable logic controller (Programmable Logic Controller,PLC), environmental information detection, vehicle behavior detection, power supply monitoring, illuminance monitoring, brightness control, communication network and LED lamps, as shown in Figure 1. When the traffic flow is large, the system is based on the open application of the protocol based on the fieldbus control system (Fieldbus Control System,FCS) for stepless dimming management of LED lamps, and the comparison of multiple tunnel lighting cases proves that its energy-saving efficiency is significantly higher than that of the graded dimming scheme.

Fig.1 "LED + intelligent" lighting architecture of highway tunnel

the environmental information * * * of the "LED + intelligent" lighting system and the vehicle behavior sensor collect the brightness, driving speed and traffic flow information inside and outside the tunnel. The illuminance detector monitors the illuminance in the tunnel in real time. The monitoring detector comprehensively monitors the working status of lamps in the tunnel, vehicle accident stay or fire, etc. The system communication is networked by optical fiber, power line carrier or wireless transmission (Wireless transmission), etc, ensure reliable and stable data transmission between equipment and stations, and ensure that the control center can understand the lighting and road conditions in real time. The control center issues regulation instructions to each subsystem after system operation processing according to the corresponding monitoring data, and the tunnel lighting system adjusts the lighting mode and brightness level according to the instructions to meet the lighting requirements.

The control device of LED tunnel lamp generally adopts constant current, constant voltage or constant power control, which often fails to reach the ideal control accuracy. Usually, a micro control unit (Microcontroller Unit,MCU) is used as a management module to integrate time control, temperature control, light control, current averaging, soft start and other technologies to realize intelligent control, and DALI, pulse width modulation (Pulse Width Modulation) are reserved according to the tunnel management scheme, PWM) and 0-10V dimming and other intelligent control interfaces. Several tunnel lighting cases have proved that the application of 0-10V dimming scheme has the advantages of wide dimming range, high power supply efficiency and stable signal transmission, and has been widely used. The working principle of the control device and intelligent control module using LED tunnel lamps is shown in Figure 2. </p>

fig.2 Schematic diagram of intelligent control of LED tunnel light

1.4 tunnel lighting with light:

the purpose of setting up enhanced lighting at the entrance, transition section and exit of the tunnel is to eliminate visual phenomena such as "black hole effect" and "visual adaptation lag" caused by the driver entering and leaving the tunnel. The enhanced lighting is turned off at night or during the time when the brightness difference between the inside and outside of the tunnel is small to avoid glare and eliminate potential safety hazards. In the design of tunnel lighting scheme, the lighting arrangement mode shall be determined according to the tunnel height and the number of lanes. Typical tunnel lighting shall be arranged according to the center line, staggered on both sides or symmetrical on both sides. The light projection direction can be adjusted according to the light distribution characteristics of the lamps. The overall lighting gradient is "U-shaped" distribution, which is more in line with people's visual characteristics to meet the needs of tunnel lighting.

Lamps and lanterns are divided into daytime lights, dusk lights, all-day lights, night lights and emergency lights according to their functions. They are used to meet the needs of tunnel lighting under different conditions, and intelligent control system is used to manage the brightness difference between inside and outside the tunnel to ensure the best energy-saving effect of tunnel driving illumination.

1.5 tunnel lighting design:

based on the particularity of tunnel lighting application conditions, LED tunnel lamps shall meet the corresponding requirements of GB 7000.203-2013 "Lamps Part 2-3: Special Requirements for Road and Street Lighting Lamps". Typical LED tunnel lamps shall be designed with modular structure, and anti-aging silicone rubber ring shall be used to seal the optical lens and body to ensure the lamps.The protection level reaches IP65 and above, the lamp meets the wind pressure resistance strength requirement that the projected area can withstand a wind speed of 150 km/h without excessive deformation, the LED module adopts a fin natural convection heat dissipation structure, and the surface nano-coating treatment is used to enhance heat radiation. The optical lens adopts the node normal vector matching method of symmetrical or asymmetrical curved surface control grid for secondary optical design according to the installation method, in order to ensure that the illumination and uniformity of the lamps meet the requirements of the corresponding sections of the JTG/T D70/2-01-2014 industry standard.

2. tunnel lighting quality:

2.1 tunnel lighting product standards:

tunnel lamps used in domestic tunnel lighting shall use control devices that have passed the national 3C compulsory certification. The safety of lamps shall meet the corresponding requirements of national standards GB 7000.203-2013 and GB 7000.1-2015 "Lamps and lanterns-Part 1: General Requirements and Tests. Electromagnetic compatibility (Electro Magnetic Compatibility,EMC) shall meet the requirements of relevant national standards, radio disturbance characteristics shall meet the requirements of GB 17743-2007 "Limits and Measurement Methods for Radio Disturbance Characteristics of Electrical Lighting and Similar Equipment", and electromagnetic compatibility immunity shall meet the requirements of GB/T 18595-2014 "Electromagnetic Compatibility Immunity Requirements for General Lighting Equipment, the harmonic current emission limit meets the standard requirements of GB 17625.1-2012 Electromagnetic Compatibility Limits Harmonic Current Emission Limits (Equipment Current Input ≤ 16A per Phase). The tunnel lighting quality shall meet the corresponding requirements of industry standard CJJ 45-2015 Design Standard for Urban Road Lighting and JTG/T D70/2-01-2014.

2.2 power density:

the lighting power density (Lighting Power Density,LPD) refers to the sum of the power of all lights installed on the unit area, and includes the power consumption of the control device and the controller. Article 7.1 of the industry standard CJJ 45-2015 has corresponding requirements for LPD. LPD is closely related to lighting energy-saving indicators. LPD requirements for different sections of the tunnel are different. Factors such as design traffic volume and vehicle speed should also be considered. On the basis of meeting the lighting requirements, LED lamps with easy light color control and high efficiency and energy saving are preferred to reduce tunnel lighting LPD.

2.3 tunnel lighting light quality:

2.3.1 Visibility

visibility reflects the difficulty of human eyes with normal vision to see clearly the outline of the target. visibility is affected by the comprehensive influence of tunnel background brightness and adjacent environment on human vision, and is one of the comprehensive evaluation indexes reflecting tunnel lighting quality. The visibility is related to the brightness of the tunnel wall, the brightness of the road surface and the flashing frequency, which directly affects the difficulty of the driver to identify the object, reflects the relationship between the visibility and the lighting quality in the tunnel, and is also an important indicator of the visual perception of the tunnel.

2.3.2 Reaction time:

the occurrence of traffic accidents in highway tunnels is closely related to the driver's reaction time, which refers to the time from seeing obstacles to taking measures. Related studies have shown that the reaction time has a direct correlation with the ambient brightness, the ambient brightness is different, the reaction time of the driver in the tunnel is not only affected by the ambient brightness, but also by the distribution of lighting, tunnel lighting design should consider how to effectively shorten the driver's reaction time from these aspects, in order to reduce the frequency of traffic accidents.

2.3.3 Brightness uniformity:

the brightness uniformity (brightness uniformity) refers to the ratio of the minimum brightness to the average brightness on the tunnel road surface, and the longitudinal brightness uniformity refers to the ratio of the minimum brightness to the maximum brightness on the lane axis. The design of tunnel lighting scheme shall use DIALux software for modeling and simulation. The brightness uniformity of lighting distribution and simulation tunnel transition section is shown in Figure 3 to ensure that the low brightness and uniformity of each section of tunnel lighting meet the corresponding requirements of JTG/T D70/2-02-2014 industry standard.

If the brightness and uniformity of the field of view are too low, the bright part will form glare, and the change of brightness and darkness will bring strobe effect, which will make the driver's visual effect worse and increase visual fatigue. When the tunnel pavement continuous and repeated bright and dark with the formation of the "zebra effect" so that the driver feels very irritable, usually longitudinal uniformity to evaluate the degree of "zebra effect", the phenomenon will seriously endanger the safety of traffic.

3. tunnel lighting operation control:

3.1 power supply guarantee:

the tunnel power load shall meet the corresponding requirements of the industry standard JTG/T D71-2004 Code for Design of Highway Tunnel Traffic Engineering issued by MOT, and the load level shall be determined by the impact or loss degree of power supply reliability and interruption of power supply on society and economy. Fire pump, smoke exhaust fan, fire detection, alarm, emergency lighting, control facilities and basic lighting all use Class I load; electromechanical equipment uses secondary load; the rest of the power and lighting use three-level load scheme. The management party shall regularly inspect the power, lighting, ventilation and fire-fighting facilities inside and outside the tunnel to ensure the stability of power supply and the safety of driving in the tunnel.

3.2 tunnel mouth dimming measures:

the lighting brightness value of the tunnel entrance and transition section is directly related to the brightness outside the tunnel. In the tunnel lighting design, light reduction measures are set at the tunnel entrance to reduce the brightness difference between the tunnel entrance and transition section and the outside. Evergreen trees are planted on both sides of the roadbed of the near section. The inner wall of the tunnel is darkened and cold-toned. The slope is greatly greened and the bamboo-cutting tunnel entrance scheme is adopted, at the tunnel entrance with the sky area ratio of not less than 50%, interval shading shall be carried out, and light reduction facilities shall be added at the tunnel entrance to ensure the safety of tunnel driving.

3.3 assessment mechanism:

highway tunnel lighting is designed according to the specific situation and the most unfavorable conditions, the best scheme of tunnel lighting dimming and operation management should be optimized, and the lighting system management scheme conforming to the characteristics of the tunnel should be formulated. Introduce a professional evaluation agency to evaluate the lighting demand benchmark of the tunnel under the environmental conditions of cloudy day, heavy cloudy day, cloudy day, rainy day, sunny day and night, and simulate the change of traffic volume and other conditions to ensure the reasonable and reliable operation of the multi-mode dimming scheme of the tunnel lighting system.

4. LED + intelligent "tunnel lighting application prospect:

the high-pressure sodium lamp used in traditional tunnel lighting is full-spectrum. When designing lamps, diffuse scattering covers should be used to refract the light to meet the lighting distribution. The new solid-state LED light source has the advantages of long service life, high efficiency, low energy consumption and easy regulation. Its luminous angle can be designed according to application requirements. When designing lamps, optical lenses are used to improve the utilization rate of light, coupled with the promotion and application of "LED + intelligent" lighting system in highway tunnel lighting, as well as the convenience of system management and simple operation, it has created an opportunity for LED tunnel lamps to be widely used in highway tunnel lighting, and to promote the innovative application of highway tunnel intelligent lighting based on "standardization, intelligence, low cost and diversification.

In the tunnel operation safety and lighting energy consumption is becoming more and more prominent, in order to ensure the improvement of lighting quality and safety and reduce energy consumption, in recent years, many high-speed main roads and typical tunnel lighting in China have adopted the "LED + intelligent" lighting system scheme, which significantly reduces the operation energy consumption and maintenance cost. At the same time, it also drives the tunnel lighting using high-pressure sodium lamps to gradually replace with LED tunnel lamps, the "LED + intelligent" lighting system with high efficiency and energy saving will be widely used in tunnel lighting.

5. conclusion:

tunnel lighting is an important part of transportation energy consumption. The mileage of highway tunnels in China is increasing exponentially, and the effect of energy saving and emission reduction of tunnel lighting has become the focus of the industry. Through the promotion and application of "LED + intelligence" in tunnel lighting, the advantages of intelligent control technology are used to optimize the energy saving of tunnel lighting. On the basis of ensuring the safety of vehicles, the energy consumption of lighting is reduced and significant economic benefits are produced. In the design of tunnel lighting scheme, through the application of multi-disciplinary technology and complementary advantages, the application advantages of "LED + intelligence" are exerted to effectively promote the efficient energy saving and healthy development of tunnel lighting.