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Discussion lighting power density of highway tunnel lighting

With economic development, highway construction has been a rapid development. Among them, since the highway tunnel has shortened mileage, save time, improve transport efficiency, save space and help to protect the ecological environment, etc., are widely used in road construction in the mountains, many grew up tunnels built one after another. At the same time, the size and number of ventilation tunnel lighting also will be growing, operating and maintenance costs are also increasing. Since the tunnel generally requires 24 hours of uninterrupted lighting, tunnel lighting energy consumption in the proportion of total energy consumption in the operation of up to 40% to 50%, therefore, how to save energy and more attention tunnel lighting, tunnel lighting energy tunnel lighting is an important research direction of design.

1. The role and significance of the tunnel lighting power density.
Lighting power density that is installed lighting power per unit area (including a light source, ballast or transformer). It took into account the power loss of the entire lighting system, more comprehensive in contrast to energy savings, science; at the same time, LPD as a relatively simple and easy to operate indicators, both for the designer implementation, but also facilitate the management of energy saving effect of acceptance evaluation . Thus, in these criteria described above, it is used as an energy-saving lighting of the LPD evaluation, and these LPD values (except residential buildings outside) are released as a mandatory provision that the requirements must be strictly enforced.

Tunnel lighting LPD value is to develop energy efficiency standards for tunnel lighting. Tunnel lighting an important way to achieve energy efficiency. Results of their research for the promotion and implementation of tunnel lighting energy saving technologies play a crucial role, but also have practical significance to ease the power shortage, reduce tunnel operating costs and building a conservation-oriented society.

2. Characteristics of tunnel lighting
Role tunnel lighting and road lighting is basically the same, both in order to ensure smooth flow of traffic and set up functional lighting, lighting its purpose is to give the driver to provide a safe and comfortable visual environment, protection of traffic operation, improve transport efficiency. However, tunnel lighting in general lighting and have a big difference, because the tunnel is a semi-enclosed space, the visual characteristics of a tunnel on the road than the road lighting is much more complicated, it requires not only 24-hour lighting, and its daytime lighting night lighting more than complicated.

Tunnel lighting and road lighting differs from place mainly in the following aspects:
1) Effect of the inner surface
It is precisely because the tunnel is a semi-enclosed space, not only has the inner surface of the tunnel road, there is also the walls and ceiling, which are generally do not have the road. In the form of spatial structure and interior lighting with some similarities, namely the ceiling and walls of the tunnel as the interior surface has a reflectivity that can improve the quality and effectiveness of road lighting, tunnel lighting has a certain contribution. Considerations of visual function and traffic safety, the tunnel lighting needs luminance walls so required, and the need to allocate part of the light flux to the ceiling and walls of tunnel walls and ceiling with a certain brightness level.

2) the impact of visual adaptation
Since the external environment inside the tunnel and the light path of the great changes, visual need some time to adapt to the situation to see the road. In order to allow the driver at both ends of the tunnel entrance to have a good visual transition, we must fully consider the human eye to light adaptation and dark adaptation problems. Thus, tunnel lighting is divided into several different lighting segments: entrance lighting, lighting transition section, the middle section lighting, exit lighting segment.

3) the impact of air quality
Inside the tunnel, due to ventilation conditions, automobile exhausts easy rapid dilution, prone to gather the formation of smog, car headlights light is absorbed and scattered the smoke, forming an obstacle in front of screens and reduced its background (road brightness, contrast, wall) between the obstacle influence visibility, adverse impact on the visual function.

3. Factors for tunnel lighting power density
The main factors for road LPD include: road lighting standard values; namely, the road width of the road lanes; road lighting characteristics of the light source. Among them, the road lighting standard values is affected by road type, vehicle speed, traffic, road surface materials and other factors.

But for the tunnel, because it has some of the above features, in addition to determining the tunnel LPD consider the main factors of general road LPD, but also must consider the following aspects:

1) tunnel walls, ceiling reflection coefficient increment
It is precisely because the walls and ceiling of the tunnel more than roads, and the brightness level and the reflection situation walls. The ceiling has a greater impact on the quality and effectiveness of the tunnel lighting. Therefore, it should be characterized tunnel road illumination improves the degree of tunnel lighting reflection coefficient taking into account the incremental tunnel lighting calculations and lighting standards.

2) cross-sectional shape and size of the tunnel
Since the tunnel is a semi-enclosed space, in the form of spatial structure and architectural interior rooms similar. In architectural lighting design, which chamber shape index (RI) and LPD room is closely related to the standard value in the illumination of the room and the selection of lamps are the same, the higher the room shape index (RI), corresponding to the standard illuminance value smaller LPD ; the lower chamber shape index RI, corresponding to the LPD standard illuminance value becomes. The same can be pushed to the tunnel. Its cross-sectional shape and size should also be closely associated with the LPD.

3) the value of tunnel lighting standards in different lighting segments
In order to ensure the driver's visual adaptation ends of the tunnel entrance, the various segments of the tunnel lighting. Lighting standards lighting different segments have different values, which also led to a tunnel with various lighting segments have different LPD values.

4) the concentration of the smoke tunnel
As previously mentioned, the tunnel will reduce the brightness, contrast and smoke barriers visibility, adverse impact on the visual function. Thus, the ratio of gasoline and diesel vehicles, ventilation, etc., that the size of the smoke concentration directly affects the quality of tunnel lighting, LPD will lead to increasing value in varying degrees.