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Why Did The LED Rise In The Tunnel Application?

Jan 18, 2018

In the vast majority of outdoor lighting applications, LED proved its advantages. For tunnel applications, the point source integrated into the solid-state lighting system is particularly matched. In this article, the Lumileds Global marketing and business development manager, Dale Kane, describes the specific challenges that the tunnels pose and how to address harsh lighting requirements by combining LEDs with lenses.


The two words "dark" and "grey" aptly describe the illumination of many highway tunnels in the world. So when you see a bright tunnel with no shadows or black dots, you may wonder why all tunnels do not have such good lighting conditions. In fact, new tunnels in many parts of the world have shown that well-designed led tunnel lighting can help drivers easily and quickly adjust their eyesight, minimize maintenance, and conserve energy while improving light quality.


We will discuss some of the items that demonstrate the value of solid-state lighting (SSL) based on led tunnels. Whether the tunnel lighting should be upgraded using LEDs, there are two main factors to consider. Municipal services generally focus on life-cycle costs and the quality of light.


The total cost of ownership of public lighting depends on illumination, power consumption, equipment cost, installation cost, maintenance cost, lamp contour size and lamp life expectancy and other factors. While other quantifiable factors may be considered, it is primarily the decision of the competent authorities.


With the maturity of solid-state lighting technology, the quality of this illumination is very good for use in tunnels. Compared with the commonly used outdoor lighting products, LED lighting has excellent color rendering.


Road users and pedestrians attach great importance to light quality. Some cities and utilities have chosen LED lighting to improve the business area, making it more attractive and more secure and comfortable.


In tunnel lighting, it can be said that total cost of ownership and visual perception are factors. However, given the state of public finances, lower total life cycle costs must be achieved. Fortunately, LED technology to reduce the LED tunnel lighting system procurement and power costs, and traditional high-pressure gas discharge (HID) compared to the LED significantly reduce the life cycle costs, but also has the other advantages of solid-state lighting systems.


Comparison of LED and traditional illumination


At present, the traditional high-pressure gas discharge (HID), such as high-pressure sodium lamp (HPS) and metal Halide lamps (MH), is still the main force of tunnel lighting. The tunnel lighting scheme requires a high minimum illumination to provide a safe environment for users. Lamps must be able to provide high levels of illumination at a distance from the plane. The typical installation height of highway tunnel is 5-7 meters, which provides clearance for high side vehicles.

High-pressure sodium lamps and metal halide lamps are very attractive to the designers of tunnel lighting schemes, providing both low unit cost and high illumination. The array of high pressure sodium lamps and metal halide lamps usually have a power of up to 400W per lamp to meet illuminance requirements.

However, the disadvantages of high pressure sodium lamps (HPS) (Fig 1) and metal halide lamps (MH) are obvious. These two lamps consume a large amount of energy, usually with low light quality, are not able to provide uniform lighting in the tunnels, and if there is a failure, an expensive maintenance plan is needed to remedy the problem. Now, with the development of LED technology, tunnel operators have a new choice, from the public and operational perspective more and more attractive.


The most obvious advantage of LED tunnel lamps is their long life and high efficiency:

In typical tunnel lighting applications, high quality LED lighting systems can provide >100 lumens/watts. As the LED is a directional point light source, its optical output can be accurately transmitted to the desired area, and hid system compared to provide additional system efficiency.

LED is a very reliable semiconductor device, the service life is very long, greatly reducing the maintenance and services costs.


Excellent lighting environment


The benefits of LED illumination in highway tunnels are mainly divided into two categories: the light quality and the reduction of the impact on traffic flow. The high quality light of LED lamps is largely due to the superior color rendering of LEDs. For example, Lumileds's ultra-high-efficiency Luxeon T LED has a minimum CRI of 70, and a common cri for high-pressure sodium lamps is 20. When comparing these two technologies, the LED based solution creates a more natural environment.

A more realistic display of colors in the spectrum can help drivers better distinguish distant objects from the orange-brown rays produced by high-pressure sodium lamps. Even with the same absolute illuminance level, the environment will feel safer and more comfortable.


Uniform lighting throughout the tunnel is another benefit of the LED scheme. Through the use of advanced optical mold developed lens design, on the road provides a uniform pattern of light, neither shielding nor interference glare. This consistency is achievable because the LED lamps are made up of small but powerful light arrays, which can form beam patterns as needed, such as using full internal reflection (TIR) lenses on each led to form the desired beam. In the entire space, smoother, more consistent lighting is formed, with no black spots or bright spots on the road surface.


Entrance lighting and export lighting


LED tunnel lamps can also enhance the light control in the transition inlet and outlet area to make the driver's eyes more adaptable. Conventional high-pressure sodium lamps and metal halide lamps are designed to simulate the illumination level of the full illumination, and to close a part or a whole section of the luminaire in one day according to the external illumination level.


If the high pressure gas discharge lamp to match the light level outside the tunnel, it will appear most of the day brightness is too bright, and the required level of illumination far away. The main reason is that hid lights can not be accurately controlled. Instead, LEDs are fully tunable and can accurately match the required lighting levels to eliminate excessive illumination and reduce energy consumption.

Because the LED is very durable, usually do not like HPS or MH lamp failure, so do not need to close part of the tunnel, erecting high-rise platforms, etc., to maintain the smooth road.