In this paper, the principle, structural composition, materials, and characteristics of solar optical fiber lighting system were discussed. The different luminance requirements of different zones of highway tunnel were identified on the basis of the analysis of tunnel lighting considering drivers’ visually self-accommodating physiological function for luminance change. Taken Huashuyan Tunnel of G109 Highway located in Hohhot of Inner Mongolia in China as the case study, the system design of solar optical fiber lighting for enhanced lighting in threshold zone of highway tunnel was made. It was indicated through calculation that the design length of solar optical fiber enhanced lighting was related to the design speed, longitudinal slope, and overhead clearance of the tunnel, and the design luminance of solar optical fiber enhanced lighting was related to the luminance outside the tunnel, the design speed, and the design traffic flow of the tunnel. Luminance analysis of the solar optical fiber lighting system of Huashuyan Tunnel was made based on the on-site experiment. Also, the 3D illuminance simulation results by DIALux software were made to indicate that the solar optical fiber lighting system in Huashuyan Tunnel still well met the enhanced lighting demand even not considering the contribution of LED lighting.
As a kind of natural light guidance system, solar optical fiber lighting can transmit natural light and make lighting based on the total reflection principle of light in fibers made of various sorts of materials like glass or plastic, which can introduce the light from natural or artificial light source into the optical fiber and make light redistribution through the transmission of optical fiber in terms of the lighting needs. Solar optical fiber lighting system has been given more and more attention internationally since 1960s for the characteristics of safety, environmental protection, and nonenergy consumption with the green light source of natural light [
However, it is rarely used in the tunnel lighting, mainly because of the considerable variability in optical properties between optical fiber lighting and traditional lighting system and the big differences in the functional lighting requirements between tunnel and other ordinary buildings. Therefore, the design method of optical fiber lighting system for the tunnel lighting cannot copy that of traditional lighting and the optical fiber lighting for ordinary buildings and cannot be applied directly in tunnel lighting either. Up to the end of 2012, 8000 highway tunnels with more than ten thousand kilometres have been built in China. Along with the increase in construction of highway tunnels, the power consumption of tunnel lighting also increased significantly. Therefore, it is becoming great important to save the lighting power consumption under the condition of safe driving and comfortable lighting. With the national supporting policies of energy saving and emission reduction, solar optical fiber lighting system has become an important part of modern energy-saving lighting and would also become a new way of tunnel lighting, with sunlight use, power saving, safety and health, and flexible design and almost without power hidden danger, light source heat, and electromagnetic interference.
Due to the special tubular structure of tunnel and the limitation of human’s visually self-accommodating physiological function for luminance change, extreme luminance contrast will occur when the car driver is driving into or pulled out of the tunnel in the daytime, generally visually causing “black hole phenomenon” or “white hole phenomenon,” which would bring great threats to the driving safety. Therefore, reinforcing lighting was needed as well in the threshold and exit zone of highway tunnels in addition to the basic lighting, making drivers’ eyes accommodate the abrupt changes of luminance from outside tunnel into the tunnel. Basic lighting system, powered by conventional power or PV and wind power generation systems, is generally installed inside along the whole tunnel and required for nonstop working day and night to guarantee the basic luminance in the tunnel. Unlike basic lighting, enhanced lighting system is installed in tunnel threshold zone generally as a supplementary lighting. According to “Specifications for Design of Ventilation and Lighting of Highway Tunnel of China (JTJ026.1-1999)”, lights need distributed installation in accordance with a certain luminance gradient in highway tunnel [
In view of the characteristics of solar optical fiber lighting changing with the outside natural light changing coinciding with the rules of the luminance level of pavement in the tunnel threshold zone adjusting with the outside luminance changing, the application of optical fiber lighting system for enhanced lighting in highway tunnel could greatly save the power consumption of tunnel lighting and maintenance cost of lighting facilities, providing the new ideas and methods for tunnel lighting design as well as further expanding the application scope of solar optical fiber lighting system. However, there are few researches in the relevant filed, especially with full consideration of the problems of the tunnel environment, the demand of highway tunnel lighting of different zones, the performance of the light source, the transmission loss, and the economic efficiency [
Solar optical fiber lighting system, mainly composed of light guiding device—collector, light transmission device—optical fiber, and light output device—light resource, concentrated the sunlight by collector and transmitted it to the places needing lighting through optical fiber or light pipe and then making diffused reflection [
The schematic diagram of the solar optical lighting system.
(a) Sunlight transmission through optical fibers. (b) Arrangement of optical fibers to make the fiber bundle.
With the development of new technology and new material, the transmission efficiency of solar optical fiber lighting system gradually improved. There were many different types of optical fiber lighting system. In our study, the materials and components of the solar optical fiber lighting system used for tunnel lighting are as follows.
As a new type of lighting system, solar optical fiber lighting system had some advantages that the traditional lighting systems could not match, while there were still some bottlenecks in the practical application, as shown in Table
Characteristics analysis of solar optical fiber lighting system.
Advantages | Energy saving and environmental protection | (1) Light source of clean energy with little energy consumption and artificial lighting power reduction during the day |
Safety and health | (1) Healthy and comfortable lighting environment of high quality by the control of the output of the ultraviolet ray and infrared ray | |
Easy maintenance | The collected light was the sunlight all by light guiding device, and it could well meet the requirements only to make good maintenance of the light guiding device of the centralized layout. | |
Flexible layout | The light output device could achieve a variety of forms of light emitting, such as dot, line, and surface, which would give the lighting design more freedom, diversity, and artistry. | |
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Disadvantage | High cost | The solar tracking device and the quartz optical fiber lighting system with high light transmission efficiency were relatively expensive, so the high cost of the one-time investment and cost performance problem were the major reasons affecting the popularization of light guide lighting system. |
Large attenuation in long distance | Although quartz optical fiber had a high optical transmission efficiency less than 200 m, but its transmission efficiency would drop to 10% for more than 1000 m. |
Based on the analysis of the characteristics (Table
The visual uncomfortableness and the visibility reduction would be caused by unsuitable luminance distribution, or the extreme luminance contrast in space or time was called glare. While in daytime especially in summer noon with very strong sunlight, the luminance contrast inside and outside the tunnel was very big. The light intensity dropped suddenly when the vehicle approach the tunnel threshold, and the drivers would have glare and black hole phenomenon visually if the tunnel lighting was not sufficient. Therefore, in order to visually adapt to the rapid changes of luminance inside and outside the tunnel, long tunnel could be divided into five lighting zones: access zone, threshold zone, transition zone, interior zone, and exit zone, as shown in Figure
The luminance requirements of different zones of the highway tunnel.
Enhanced lighting system needs to be installed in tunnel threshold or exit zone to make the high luminance outside the tunnel gradually decreased to the low luminance level inside the tunnel, which would make good luminance transition and improve the visual environment in the tunnel through making driver’s eyes adapt to the light intensity changes from outside to inside the tunnel and eliminate the driving safety hidden troubles visually.
The solar optical fiber lighting for highway tunnel provided the enhanced lighting through the light guiding device to collect the sunlight and transmit it by optical fiber to the reflector panel of light output device, as shown in Figure
The system design schematic of solar optical fiber lighting for highway tunnel.
Based on the analysis of the characteristics of solar optical fiber lighting system and the lighting requirements of tunnel lighting, the position of the tunnel threshold zone had natural advantage of employing the sunlight. Solar optical fiber lighting system well accorded with the law of the luminance of pavement in tunnel threshold zone changing with the changes of luminance outside the tunnel and could save considerable lighting energy consumption, so it would have certain feasibility in enhanced lighting of highway tunnel.
In this paper, we took Huashuyan Tunnel of G109 Highway located in Hohhot of Inner Mongolia in China as the case study, where it belonged to the area of the light climate zone II with the regional annual average illumination of
According to “Specifications for Design of Ventilation and Lighting of Highway Tunnel,” the distance of the tunnel threshold zone could be calculated according to the following formula:
The stopping sight distance
The stopping sight distance
Design speed (km/h) | Longitudinal slope (°) | ||||||||
---|---|---|---|---|---|---|---|---|---|
−4 | −3 | −2 | −1 | 0 | 1 | 2 | 3 | 4 | |
100 | 179 | 173 | 168 | 163 | 158 | 154 | 149 | 145 | 142 |
80 | 112 | 110 | 106 | 103 | 100 | 98 | 95 | 93 | 90 |
60 | 62 | 60 | 58 | 57 | 56 | 55 | 54 | 53 | 52 |
40 | 29 | 28 | 27 | 27 | 26 | 26 | 25 | 25 | 25 |
Because of the high requirement of the tunnel lighting, especially the pavement luminance in the threshold zone as the highest luminance in the tunnel lighting, the design luminance of solar optical fiber enhanced lighting in the threshold zone could be calculated according to the luminance outside the tunnel, the design speed of the vehicle, and the design traffic flow, as shown in the following formula:
The reduction coefficient of the luminance in the threshold zone
Design traffic volume |
| ||||
---|---|---|---|---|---|
Design speed (km/h) | |||||
Two-lane two-way traffic | Two-lane one-way traffic | 100 | 80 | 60 | 40 |
≥2400 | ≥700 | 0.045 | 0.035 | 0.022 | 0.012 |
≥1300 | ≥360 | 0.035 | 0.025 | 0.015 | 0.01 |
Because Huashuyan Tunnel in this study had two-lane one-way traffic with the design traffic volume
The solar optical fiber lighting system contained the sunlight collector, quartz optical fiber for light transmission, and fiber optic irradiator. The sunlight collector was employed in the basis set of 330DS type of Sunshine Masters Series (530 mm in diameter) including acrylic shield, light trap, and circular prismatic diffuser.
According to the above calculation of the design length of the threshold zone of Huashuyan Tunnel, the total length of solar optical fiber lighting system for Huashuyan Tunnel was 30 m, and the design luminance was set over 83.47 lux. The number of optical guiding devices was determined taking the orientation of the tunnel, the width and height of the tunnel, and the environmental factors outside into consideration. A total of 5 light pipes were installed and the solar optical fiber irradiators were installed at 10 meters from the entry of the tunnel with an interval of 5 meters to the interior tunnel, as shown in Figures
Design diagram of solar optical fiber lighting system in vertical zone of Huashuyan Tunnel.
Light pipe installation in vertical zone of Huashuyan Tunnel.
Design diagram of solar optical fiber lighting system in plan zone of Huashuyan Tunnel.
Light pipe installation in plan zone of Huashuyan Tunnel.
The onsite luminance experiment was carried out every hour from 6:30 to 16:30 for 5 consecutive days from April 6th to April 10th. Based on the sunny and cloudy condition in spring in Hohhot, the average luminance effects comparison of the solar optical fiber lighting with LED lighting in the central line of the tunnel was made in Figure
The average illuminance of solar optical fiber lighting in tunnel threshold zone in daytime in April.
We also used DIALux software to make a luminance simulation to analyze the feasibility of the solar optical fiber lighting system for Huashuyan Tunnel enhanced lighting. The luminance simulation was based on the sunny weather conditions with the outdoor average luminance of 45000 lux. The isolux distribution map with the ratio of 1 : 251 and the illuminance of solar optical fiber lighting system in Huashuyan Tunnel was shown in Figure
The illuminance of solar optical fiber lighting system in Huashuyan Tunnel.
Light pipe | Average illuminance (lux) | Maximum illuminance (lux) |
---|---|---|
Number 1 | 1065 | 806 |
Number 2 | 890 | 728 |
Number 3 | 841 | 698 |
Number 4 | 794 | 635 |
Number 5 | 710 | 582 |
The isolux distribution of solar optical fiber lighting system in Huashuyan Tunnel.
The 3D illuminance simulation of solar optical fiber lighting system in Huashuyan Tunnel was shown in Figure
The 3D simulation illuminance of solar optical fiber lighting system in Huashuyan Tunnel.
We used the quartz multimode fiber with the diameter of 1 mm available for visible light transmission in the study, which had the attenuation of 20 dB/km in the visible region and realized the practical applications of optical fiber lighting within the range of 200 m. The relationship between the transmission efficiency and the length of optical fiber could be calculated according to the following formula and the transmission efficiency of the optical fiber at different length could be obtained as shown in Table
The transmission efficiency of the optical fiber at different length.
Length of optical fiber | 10 m | 15 m | 20 m | 25 m | 30 m |
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Transmission efficiency | 95.50% | 93.33% | 91.20% | 89.13% | 87.10% |
The transmission efficiency of the optical fiber at different length.
The transmission efficiency of the optical fiber at different length could be obtained as shown in Table
It could be seen from Figure
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Therefore, solar optical fiber lighting technology was proved to have a good application prospect in tunnel enhanced lighting by improving the quality of tunnel lighting, saving electrical energy and environmental protection.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The research work was supported by National Natural Science Foundation of China under Grant no. 51108216 and the Fundamental Research Funds for the Central Universities no. 2015JBM067 and no. 2015RC023. The authors are very grateful for the helpful comments and criticisms of the anonymous reviewers.