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Tunnel Lighting Design

Outdoor Tunnel Lighting Solutions

Unlike usual road lighting, tunnel lighting has its unique particularity, especially in the presentation of the safety of tunnel lighting system.

When making a lighting solution for tunnel light, the most important element to consider is the clear-dark conforming of human’s eye, special attention should be paid on the lighting design of changeover portion. In order to sacrifice the conforming requirement of human’s eyes; a changeover portion (from clear to dark) should be made in the entrance of tunnel, to make sure people can see things clear by light changing. For the exit of tunnel, the conforming period is very short, normally within 1 second, so no need to do other dispose.

Tunnel is an enclosed area, so natural light could not get into there. To confirm the connection of driving and life safety of people in the vehicle, tunnel lighting is an indispensable part of tunnel building because even daytime, the whole tunnel need electrical lighting inside.

The discussion of energy-saving new lighting source have been focused on by the lighting industry, especially for LED tunnel light, which have been paused for a while. According to clear vision and intermediate visual theory, the relationship of CRI and LUX, LED has advanced advantage when applied in tunnel light. In this way, many important tunnel light project use LED light for light source in domestic market. There are breakable pause when LED light apply for tunnel lighting project, yet there will be some problems. For example, if there is no specialize design and construction standard when use LED as lighting source for tunnel light, it will cause the variety range of quality from good to bad. In Europe, 60% tunnels are in Italy; this case is an application of a tunnel in Roma, Italy.

Bad environment, such as vehicle exhaust, noise, vibration, pure air, etchant gas, will cause the specialty of tunnel lighting. For a safe and warm lighting circumstance to passing vehicle and passengers, we will discuss the design thought and method with analysis.

Outdoor Tunnel Lighting SolutionsUse Semlight LED tunnel light:

LED we use now for tunnel light have reached 114-122lm/W,with the electrical voltage of 3.2V, we still apply 320hA for power supply, so the practical working power is 1.024W, the total power of 56pcs is 61.6W, Upon 86% of power efficiency, the total power is 72.6W. Within 736meters tunnel, there will be a need of 103 pcs tunnel light, which total power is 103*71.3=7374.8W. Calculated with 24hrs per day as working time, the total power consumption will be 215.3Kwh per day, annual power consumption will be 71950 Kwh.

As I did not receive the LED tunnel light installation drawing before, so I designed the lighting solution for tunnel length of 700 meters, till now the practical length is 736 meters. For this, I make new adjustment, and also, consider that the brightness of tunnel light near the entrance is controlled intelligently, not with night-off method of traditional HPS light; I must readjust install density of light according to the brightness in the air. Base on the HPS install plan, lighting area of the high power light will be separated into three luminance area. From entrance to 30 meters distance is high bright area, the illumination reaches 80Lux.;From 30 meters to 60 meters is medium bright area, the illumination reaches 50Lux; From 60 meters to 96 meters is transition area, the illumination reaches 40Lux. The middle of tunnel is low bright area; the illumination only requires 30Lux. When the night comes, the bright lights turn-off, the whole tunnel become low bright area, the illumination should be around 30Lux.

When adopting light with LED tunnel light, 103 pcs LED tunnel lights will be applied in the whole tunnel. 40 pcs tunnel light near the entrance and exit of tunnel will be controlled intelligently, used to adjust the brightness. 63pcs in the middle will work with full-mode all the year around. Total amount will be 103pcs, 7pcs more than previous solution.

Detail: to install light sensors to collect light data in the entrance and exit place of the tunnel, the light data can directly control a total of 40 units LED tunnel light in the entrance and exit place to adjust the brightness. It will work with full power and full brightness in the day time and work with half power and half brightness at night. The brightness will be adjusted by external environment change. The sensor does not cost energy. In the day time, outside the tunnel is of very bright light, LED tunnel lights will work with full power in the entrance, the brightness will reach 80, 50, 30 LUX. At night LED tunnel lights will work with half power, the brightness of tunnel is about 30 LUX while the whole brightness is about 40 LUX. If you do not demand changes in brightness with the change of environment, LED tunnel lights can be directly settled up a fixed time to change the brightness.

There are several special vision problems in the tunnel.

a. Before entering the tunnel (day time): the brightness difference is very big between the tunnel outside and inside, it will come out “black hole” in the entrance of the tunnel when the brightness is insufficient.

b. After entering the tunnel (day time): the car gets into the dark tunnel from very bright environment, it needs to take a time to view the situation clearly, and this is so-called “comfort retardation”.

c. The exit of tunnel (day time): it is very bright in the outside of the tunnel exit at day time when the car passes the long tunnel, the exit looks like “white whole” and the strong glare will emerge. The driver will feel very uncomfortable. Night time is opposite to day time, it looks like a black hole but not bright hole on the exit, the driver will not view the line and roadblock clearly on the road.

Several specific vision problems above show the tunnel lighting a higher request, effectively dealing with these vision problems can follow the below aspects.

1). Tunnel lighting design.     The tunnel lighting can divide into five sections: lead-in section, conforming section, transition section, basic section and exit section; each section has played a different role:

(1)Lean-in section: Eliminate the "black hole" phenomenon, so the driver can identify obstacles at the exit of the hole; For example, assume at daytime that the brightness on the tunnel mouth environment at 4000cd/m2 and speed at 80KM / H, then the lead-in section meets the minimum request on the length at 40m and brightness at 80cd/m2.

(2) Conforming section: After entering the tunnel, the driver can quickly adapt to the light in the tunnel and eliminate "black hole" phenomenon; according to the above conditions, the length and luminous intensity on confirming section is at 40m and 80 ~ 46cd/m2.

(3) Transition section: the driver will gradually adapt to lighting inside the tunnel; according to the above conditions, the length and brightness on transition section is 40m and 40 ~ 4.5cd / m.  

(4)Basic section: it is the basic lighting inside the tunnel.

(5)Exit section: In the daytime, it gradually makes the driver adaptable to the exit of the strong light to eliminate the "white hole" phenomenon; at night, it makes the driver in the tunnel to view clearly the linear path and road obstacles to eliminate exit " black hole "phenomenon. Common practice is outside to use the street lighting as a continuous lighting.

In the daytime, the luminous intensity at the exit and at the entrance should be higher than the basic section. At night, on the contrary, the luminous intensity should be lower than basic section. When the outside of the tunnels has the street light lighting, the brightness on inside tunnel surface should not be less than 2 times the outside tunnel’s ground.

Outdoor Tunnel Lighting Solutions2).The problems on motor vehicles passing through the tunnel

(1)Problems when accessing the Tunnel

Black hole phenomenon     In the daytime, eyes of motor vehicle driver's has adopted to natural light of abve100000 lx and several thousand cd/m2, when the drive went into the tunnel environment with brightness of only a few cd/m2, appearing conform hysteresis and will see a black hole, due to the human eyes’ poor perception of brightness is limited, which can not identify the state. In this way, people can see a black hole in the bright lighting environment called “Black hole phenomenon”. Once presenting black hole phenomenon, with the vehicle close to the tunnel, the driver's visual interval shortening, can not drive safely. Black hole is the phenomenon of visual problems before the entrance to the tunnel and is the most important issue to solve when design tunnel lighting. To avoid the black hole phenomenon, the beginning of the tunnel entrance section of intervals must ensure sufficient brightness; the length of the whole part is slightly longer than the vehicle's safe braking intervals.

When entering the tunnel, there is a big brightness difference between the outside and inside, adaption will be delayed, the driver cannot adapt to the tunnel brightness quickly, it is hard for them to see the interior of the tunnel clearly. To avoid this situation, the brightness of the entrance should be decreased with the vision complying speed, in a smooth transition, reduce the brightness step by step, yet the brightness level comparison before and after shall not exceed the ratio of 3:1, by the same time, the brightness of the wall below 2m height can not be lower than the corresponding uniform surface brightness.

(2)Problems during the process of going through the tunnel     The brightness in the tunnel is higher than in the road at night, even in the daytime, but lower at night than at daytime. Considering the vehicles offgas in long tunnel with heavy traffic, the offgas change to smoke because cannot be dispersed, the smoke absorb the light and scatter, reducing visibility, which make visual identification difficult. Vehicle exhaust has great impact on the light of front rear, which can not meet the visual recognition demand. If the brightness in the front 100m road decreased to half, it is usually need 2 times the brightness of the road lighting for compensation of exhaust gas.

(3)Problems when closing to the tunnel exit     The external brightness is very high by watching from the exit, the exit appears to be a bright hole, showing a serious glare, exit become a white cave, which is called white hole phenomenon; Take bright holes as the background, motor vehicles become a black silhouette and is easy to identify. However, the silhouette of large vans with the back of cars and trucks is hard to see, close to the tunnel exit of heavy traffic load, the lighting made in order to identify overlap of big or small vehicles is called exit lighting; the interval length of exit lighting is tens of meters.

(4)Problems before driving out of the tunnel during night    During night, before exit from the brightened tunnel to the road without lighting, external tunnels become a black hole could not see the road alignment and the existing obstacles. Then, in order to reach the appropriate level of brightness, it should stop the lighting on the road of tunnel exit, greater second than the safe braking interval, roughly equivalent to a few seconds of motor vehicle driving range.

3).Application of LED products in the Tunnels     LED used in LED tunnel lighting complete the intelligent automatic dimming control system , which can adjust the illumination intensity automatically as per the light of tunnel. Compared with the traditional plan, electric saving 50% and the life of light source is 6-8 times than traditional tunnel lamps; reduce light loss and the cost of routine maintenance greatly.

Outdoor Street Lighting Solutions

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Outdoor Street Lighting Solutions

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