Highway tunnel lighting system design

Abstract: As a special section of highway, highway tunnel has the characteristics of serious pollution and high noise, which reduces the traffic capacity of the road and threatens the driving safety of the vehicle. In order to improve the traffic capacity of this bottleneck section and ensure safe driving, it is necessary to design a tunnel lighting system.

When a car driving on a highway passes through a long tunnel, the human physiological characteristics determine the subtle changes in the driver's vision, especially during the day. When the car approaches the tunnel, the ambient brightness suddenly changes from high to low, and the driver will visually appear a "black hole effect", which is extremely unfavorable for safe driving. When the car drives out of the hole, the brightness of the environment changes rapidly from weak to strong, and the glare appears visually uncomfortable. Tunnel lighting mainly focuses on how to solve the "black hole effect" when the driver enters the tunnel entrance and the "glare" problem when exiting.

1 Road tunnel lighting design

The lighting system of the road tunnel is to transmit the necessary visual information to the driver to prevent traffic accidents due to insufficient visual information, thereby improving driving safety and increasing comfort. The significant difference between tunnel lighting and road lighting is that lighting is also required during the day, and daylighting problems are more complicated than nighttime.

In order to improve the traffic capacity of this bottleneck section and ensure safe driving, it is necessary to set up a spot lighting system. The main contents of tunnel lighting include visual features, lighting design, lighting calculation, lighting control, lighting power supply and lighting economic analysis and energy saving.

The brightness of the tunnel mainly depends on the speed of the driving, the traffic flow and the brightness outside the hole. These factors have been fully considered in the lighting design process, and are generally considered in accordance with the unfavorable conditions, so it can meet the design speed, design vehicle flow and design. Lighting requirements for external brightness conditions. The brightness outside the hole is different in each season and time. Tunnel lighting control is based on these different conditions, to turn on and off the corresponding number of lamps to increase or decrease the brightness, so that it can meet the needs of safe driving, but also conducive to energy saving. The tunnel lighting control system consists of a lightness detector, a traffic flow detector, a tunnel area controller, a lighting control computer, a tunnel lighting fixture, a lighting distribution cabinet, a lighting distribution box, and a lighting power supply cable. The tunnel lighting system consists of lighting fixtures, lighting distribution boxes and power supply lines, which are controlled by different lighting circuits through the lighting distribution box.

According to the requirements of visual adaptation, the tunnel illumination area consists of an introduction section, a transition section (transition section I, transition section II, etc.), a basic section and an exit section. Tunnel lighting calculations are also naturally carried out in stages. Due to the influence of smoke and dust, the reflection rate of the tunnel wall is low. When calculating the illumination and brightness, only the direct action of the light source can be considered. The quality of tunnel lighting is currently mainly evaluated by road illuminance and brightness values.

1.1 Calculate the illumination by point by point

The illuminance at a point on the road surface is superimposed on the illuminance produced by the street lamp at this point (the illuminance produced by other sources is negligible). The total illuminance at point P is:

Where, I γc is the intensity of the luminaire pointing in the direction of point P, the direction is represented by angles r and c; n is the number of street lamps; h is the installation height of the street lamp.

The luminosity data chart of the general street lamp gives the equal light intensity curve. According to the direction angles γ and c corresponding to the P point, I γc is found on the curve, and the sub -type (1) can be obtained to obtain a street lamp to generate the P point. Illumination E p .

For ease of calculation, an illuminance curve is often created. If the position of the calculation point relative to each lamp has been determined, the relative degree of the point can be read directly from the map. Then the absolute value of the illuminance of the point is obtained by the following formula:

Where Σep is the sum of the contrasts produced by each lamp at point P; α is the specific coefficient of all lamps, given by the isograph; φs is the luminous flux of each street light source, LM; h is the installation height of the street lamp, m .

The initial illuminance value is calculated according to the formula (2), and the maintenance coefficient is calculated to maintain the illuminance.

1.2 Average illumination calculation

When calculating the illuminance on a part of the road surface, the average illuminance over this area can be obtained by:

Where E p is the illuminance of regularly distributed points on the road surface; n is the total number of calculated points. Obviously, the more points you consider, the more accurate the calculated average illumination.

Calculating the average illuminance on a road worth infinitely long, it is convenient to use the coefficient method. Its calculation formula is:

Where φ s is the luminous flux of the source, Lm; N is the number of light sources in each street lamp; K is the maintenance factor; ω is the road width; S is the spacing of the street lamps; N is the street lamp arrangement, single row, staggered N =1, the two sides are arranged N=2; U is the street lamp utilization coefficient (check the utilization coefficient curve).

The utilization factor in road lighting is defined as the ratio of the luminous flux φ' on the road surface to the total luminous flux φ emitted by the light source within the illumination range of a street lamp, namely:

The utilization factor of the luminaire in the luminosity data of the luminaire is given by curve and icon.

The tunnel lighting system is a multi-light source system. These lamps can usually be controlled by component loops. The brightness of the holes is determined by the number of lights that are turned on, and the dimming control of a single lamp is not performed. The lighting system can adjust the inner lighting system in real time according to the brightness value inside and outside the tunnel hole actually measured by the illuminometer to meet the driver's need to adapt to the difference between the inside and outside of the hole.

When the photodetector fails, the monitoring center computer can automatically transfer to the timing control, that is, the brightness value outside the hole is input into the computer according to the statistical rules obtained by daily, weekly, monthly, and annual measurements, and the computer adjusts the lighting fixture in the control hole to adapt to this. The change in value. In addition, the lighting system is also equipped with manual control functions, which can be completed separately in the central control room computer or tunnel lighting distribution box. The manual devices on the tunnel low-voltage power distribution cabinet are mainly used for maintenance.

At present, the existing light sources for tunnel illumination mainly include high-pressure sodium lamps, metal halide lamps, fluorescent lamps, and the like. LED is a new type of light source that has developed rapidly in recent years. It has the advantages of long life, high luminous efficiency, high color rendering index, directional illumination, environmental protection and energy saving. LED lighting lamps made of high-power LEDs have obvious advantages compared with other light source lamps. Advantage, but its cost is higher than other light source lamps.

However, with the development of LED technology and technology, the performance indicators such as light efficiency are rapidly increasing and the price is rapidly decreasing. The improvement of light efficiency means the improvement of energy utilization efficiency, so that in the successful application of display, landscape lighting, etc., in road lighting Equally directional lighting has also begun to gradually gain application.

At present, the reliability of high-power LED tunnel lights generally faces two major problems: 1 reliability and life of the drive power; 2 rapid heat conduction of the heat dissipation system. Among them, the reliability of the driving power supply accounts for more than 60% of the reliability of the LED tunneling lamp. Due to the instability of the previous LED driving power supply, the development of the LED lighting industry chain has been delayed by at least 1 to 2 years. The existing high-power LED tunnel lamp driving power source has the following three types: constant voltage mode; constant current mode; constant current plus constant voltage mode.

Since the change in light within a certain range of brightness is not perceptible or substantially imperceptible, the current of the LED is allowed to vary within a certain range. When people began to understand the use of constant current sources to power the LEDs, some people went to extremes, thinking that if it is not "pure DC" (ie, DC without ripple), it will damage the LED. This is another new misconception about LEDs. In fact, as long as the operating current of the LED is in the safe working area, the current fluctuates, as long as the peak power is still in the safe working area, it will not affect the LED. For example, with a stable current of 10 mA and a square wave with a peak value of 20 mA and a duty cycle of 50%, the LED current is very unstable, but its effective value is only 10 mA, and the lifetime is not higher than The difference in current is 10 mA. Therefore, the LED operating in the safe working area, the unstable current does not affect the life of the LED, but it will affect the stability of the light, as long as the fluctuation of the control light is under the threshold of the human eye feeling flicker, then such a small Light wave fluctuations have no effect. Furthermore, with an illumination source in which a plurality of LEDs are combined, since the brightness of the light source is large, people do not always stare at it, so there is no problem even if there is a certain difference in brightness between each LED. According to the above analysis, it can be recognized that it is not necessary to use a constant current source to supply power to the LED, but to specifically select and design the driving circuit according to the performance requirements of the actual light source.

When the LED production process matures, the energy-saving advantages of LEDs will be highlighted in comparison with traditional tunnel illumination sources. LEDs are now mostly used in mountain road tunnels. The application effects are different. There are still many problems in the application, such as high light decay, high junction temperature, unreasonable lamp structure, poor illumination uniformity, driving power supply life, and uneven quality. Therefore, the design tells road tunnel LED lighting. Application needs to strengthen system research and gradually form technical standards to ensure the feasibility of LED application in tunnel engineering.

2 Conclusion

The economics of lighting is also an important indicator after fully considering the completeness of the lighting system. The economics of lighting system equipment are studied to minimize the cost per unit of illumination under the same lighting conditions. There are many factors affecting the economics of lighting, including useful electricity, equipment, construction and maintenance. Therefore, it is necessary to find a good analytical calculation method and promote the use of a new generation of LED cold light sources. Consider it in the planning and design.

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