Huang Zheng
(Jiangxi Ganyue Expressway Co. Ltd.)
Wu Changhua
(Jiangxi Fangxing Science & Technology Co. Ltd.)
Chen Wencheng, Lin Yandan, Guo Liping, Chen Dahua
(Institute of electric light sources, Fudan University,Shanghai)
Li Weide, Wang Aiqun
(Shanghai Hongyuan lighting & electric Equipment Co. Ltd.)

Abstract
The characteristics and performance of two tunnel lighting systems are investigated in this paper. Tunnel No. 1 is installed with induction electrodeless fluorescent lamp (IEFL) and tunnel No. 2 is installed with HPS lamps. The luminance levels and illuminating uniformity with two systems were measured and analyzed. The color rendering and energy cost have also been studied. Additionally, the responses of drivers were investigated. By the comparison of these two tunnel lighting systems, it was found that the tunnel lighting system with induction lamps shows great advantages in high brightness perception, good color rendering, higher uniformity, better safety perception, low energy cost, over the tunnel lighting system with HPS lamps.
Key words: Tunnel Lighting, induction lamp, HPS lamp, IEFL

1. Introduction
China has a land area of 9 600 000 km2. The high plateaus and mountainous areas cover approximately 65% of the land. With the great development of economy and technology in China, tunnel constructions have increased significantly since 1990s. According to the statistics from Ministry of Communication of China, until 2004 the total length of tunnels in China, including railway tunnels, road tunnels and underwater tunnels, is around 6000 km with an increasing rate of 300 km/year. The total length of road tunnels is about 704 km. The longest road tunnel is ZhongNanShan tunnel with a length of 18.4 km which is still under construction . Different from railway tunnels and underwater tunnels, the driving conditions of road tunnels are more easily affected by tunnel lighting, weather, traffic flow and so on. But efficient road tunnel lighting can significantly improve the visibility of drivers even in poor weather conditions or heavy traffic flow. According to the CIE technical report 88-1990, the goal of a quality road tunnel lighting system is to "ensure that traffic, both during day and nighttime, can approach, pass through, and leave a tunnel, at the designated speed, with a degree of safety and comfort not less than that along adjacent stretches of open road".[1]
At present, fluorescent lamps and HID lamps are the lamps that are most widely used in road tunnel lighting, not only in China but also in most other countries. Fluorescent systems, although capable of providing excellent illumination quality, can be difficult to maintain and the life time of fluorescent lamps is short which results in high maintenance cost. Conventional HID fixtures can facilitate quick lamp change, but illumination quality can be compromised by the poor color rendering [2].
The induction electrodeless fluorescent lamp (IEFL) is fundamentally different from the traditional discharge lamps, which employ electrodes as electron source. A long life time and good lumen maintenance can be achieved with this kind of lamps because of the absence of electrodes. Roadway tunnels typically present a tremendous maintenance challenge for the responsible authority. The harsh environment results in a short life for many luminaire designs, and lane closures required for relamping and other routine maintenance can be costly and highly problematic to the flow of traffic [6]. With high efficiency, good color rendering and extremely long lamp life, IEFL can be a better solution for tunnel lighting comparing with conventional fluorescent lamps and high pressure sodium lamps.
In order to get an optimized design for tunnel lighting, a comparison is made between two tunnel lighting systems, which are installed in Jiangxi Province, China. One of the tunnels is installed with induction electrodeless fluorescent lamps and the other is installed with high pressure sodium lamps. In order to investigate the performance of two tunnel lighting systems, experiments were taken to measure the luminance levels and uniformity. Meanwhile, the color appearances of two lighting systems were compared and the energy cost was also taken into consideration to evaluate the performance of lighting systems. A survey was taken for the drivers’ opinions on both tunnel lighting systems. So that the evaluation method is comprehensive in this paper.
2. Construction of the two tunnel lighting systems
In this paper, two tunnel lighting systems are investigated. The two tunnels are located in Jiangxi Province, China. An important expressway goes through these two tunnels. Both of the tunnels are single-line and have two lanes.
As shown in figure 1, the tunnel on the left side is installed with induction lamps, which is named with tunnel No.1 in this paper. And the other one on the right side is installed with high pressure sodium lamps, which is named with tunnel No.2. Tunnel No.1 is located north to the tunnel No. 2. Because both tunnels are single way and traffic goes along the right side in China, traffic only goes from east to west through tunnel No.1, and from west to east through tunnel No.2. The length of tunnel No. 1 is 0.885 km, and tunnel No. 2 is 0.74 km.

Fig.1. Picture of the Tunnel No. 1 and No.2
The total width of each tunnel is 10.25 m, which includes the motorway and sideways. The width of motorway is 8.5 m, and the width of sideway is around 1 m on both sides, which is for the convenience of maintenance.
The selection of lamps is decided according to different lighting requirement for the five key areas. The detailed installation information is shown in table 2. The luminaries are installed symmetrically. Interval of two luminaries is 8 m.
The critical task facing the driver approaching the tunnel entrance portal during the daytime is to overcome the “black hole” effect created by the high ratio of external to internal luminance. In order for the driver not to lose his visual ability, and carefully taking the dark adaptation of the eye into account, it is necessary to have intensive lighting in the threshold zone of the tunnel [7]. From the installation information in table 1, we can see that the threshold zone of each tunnel has the most intensive lighting by employing two 200 W induction lamps or one 400 W lamps. Then the transitions zones have less intensive lighting so that ‘black hole’ effect can be avoided.
Table 1 Installation information

? Although the principles of electrodeless lamp have been understood essentially for over hundred years, electrodeless lamps have not been introduced into the commercial market until the past decades. The main reasons are the lack of reliable, low cost electronics, and avoidance of electromagnetic interferences. With the great development in electronics and consequently arrivals of electronic ballasts, the electrodeless lamp got the possibilities to be introduced into commercial market for the general purpose lighting [4]. The appearance and polar curves of IEFL employed in the tunnels are shown in figure 2.

a)--------------------------------------------------- b)

Fig.2. a) Appearance of luminaire of IEFL b) Polar curves of luminaire of IEFL

Because this is the first time that IEFL is employed in tunnel lighting, the applicability of IEFL in tunnel will be investigated by the comparison between IEFL and the most popular used light source, HPS lamps. The essential characteristics of HPS lamp and IEFL are listed in table 2.
Table 2. Essential parameters of two kinds of lamps

The parameters listed in table 3 show great advantages of IEFL in longer lamp life, better power factor, lower maintenance cost, and better color rendering than HPS lamps. The luminance efficacy of IEFL is lower than HPS lamp. But IEFL with luminance efficacy of 60~80 lm/W is still a very efficient light source with excellent color rendering.
3. Evaluation of the two systems
3.1 Experiment
The evaluation of a tunnel lighting system has to consider the effects of luminance level, uniformity, color rendering, safety perception, energy consumption and so on.
In our experiments, luminance levels in different zones were measured and the uniformity of the road surface was calculated. The results are shown respectively in table 3 and table 4. In addition, the color rendering of the two tunnel lighting systems are also investigated and the energy consumption issue is also studied. The measurements were carried out by the highway testing institute of Chongqing, China and the institute of electric light sources in Fudan University, China.
Table 3. Luminance levels of the two tunnel lighting systems in daytime

Note: The recommended luminance values represent the lowest in-service values that should be allowed throughout the operation life of the system. The real luminance values have considered the maintenance coefficient.

Figure 3. Luminance levels of two tunnel lighting systems

The recommended luminance value in table 4 is decided by the guidelines of road designing of China. It can be seen more clearly from figure 3 that the luminance levels in different zones with IEFL are very close to the recommended values. Obviously the luminance levels of HPS lamps are higher than those of IEFL in different zones. It must be clarified here that higher luminance level does not directly lead to better tunnel lighting quality. For instance, in the interior of a lighted tunnel, where luminaries or their reflected images are in view of drivers, the flicker effect of passing closely spaced light sources may produce undesirable behavioral sensations [8]. The significance of this effect depends on the brightness of the source to the observer and the rate at which light sources appear to be moving. In this case, the higher luminance level will result in more significant flicker effects.
Table 4 lists the uniformity of two lighting systems. It is clear that the overall uniformity and longitude uniformity of tunnel No. 1 with IEFL are much higher than the recommended values and HPS lamps. It is no doubt that the higher the uniformity is, the better lighting system is.
Table 4. The uniformity of road surface with the two tunnel lighting systems

Color rendering is also an important issue to evaluate the quality of tunnel lighting system. As well known, the main drawback of HPS lamps is poor color rendering while IEFL offers much better color rendering with CRI=84. From figure 4, we can easily see the color difference between the white light in tunnel No.1 with IEFL and poor yellowish light in tunnel No.2 with HPS lamps.?

a. Tunnel No.1------------------------b. Tunnel No. 2
Fig 4. Color rendering of two tunnel lighting systems

Energy cost is a very practical consideration in the evaluation of tunnel lighting. With the aid of power meter, energy consumptions of each tunnel lighting system have been recorded. It was found that 12.8% of energy savings can be achieved with IEFL comparing with HPS lighting system.???????
3.2 Drivers' opinions for each system
The opinions of tunnel users’ on the lighting systems can be affected by the luminance levels in different zones, color rendering of lighting, uniformity of road surface, etc. Although the opinions can not show exactly how much light there is, they can indicate the quality of lighting system in some sense.
In order to evaluate users’ opinions on lighting performance of the two tunnel lighting systems, 193 drivers were asked to do a short questionnaire containing three questions. The person-to-person approach ensured that the respondents could understand the questions and thereby achieve accurate responses. The questions are listed in table 6. The responses are listed in table 7.
Table 6. The questionnaire for the drivers

Table 7. The answers of the drivers

The answers of the drivers obviously show that the lighting system with induction lamps has better performance such as in offering brightness perception and safety driving environment. So it is more preferred and attractive for most drivers with the lighting system of induction lamps.

4. Conclusions
In order to get an optimized tunnel lighting solution, the performance of two tunnel lighting systems, installed with traditional HPS lamps and induction lamps respectively, was investigated and compared. It was found that tunnel lighting system with induction lamps offers better photometric characteristics over HPS lamps, such as good color rendering, higher overall and longitude uniformity in key areas of the tunnel. Meanwhile, induction lamps have high luminous efficacy and extremely long lamp life and they are almost free of maintenance. These features result in low energy consumption and low maintenance cost. By the questionnaire to drivers, it was found that drivers are more satisfied with driving conditions in the tunnel lighting system with induction lamps because they can feel more brightness and safety in the lighting environment produced by induction lamps. So tunnel lighting with IEFL is an optimized solution which is economically efficient and also provides most effective lighting.
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