But tunnels can be challenging for drivers. Serious traffic congestion is a perennial issue for tunnels. And while crashes are less common in tunnels than they are on open roadways, they’re also often far more serious, for obvious reasons, including the inaccessibility of tunnel accidents for emergency crews.
 

Then there’s the feeling of comfort and safety. A drive through a darker and more monotone area can in itself create a negative experience for drivers. When lighting conditions are inadequate, the situation can get even worse, seriously impacting visibility and the driver’s sense of safety. Tunnel entrances, for example, can subject drivers to the unpleasant and also highly dangerous “black hole effect,” the effect drivers experience as they hurtle from broad daylight towards a tunnel’s dark mouth in the absence of an appropriate lighting level in the entrance zone. In fact, a tunnel’s entrance and exit zones are its most dangerous, exploiting the human eye’s inability to adjust fast to different amounts of light.
 

What follows is a checklist for lighting professionals to follow as they plan tunnel projects. The goal is to make the act of driving through a closed passage as safe and pleasant as possible while ensuring compliance with local standards, offering better control, and allowing the deployment of an efficient maintenance plan.

Maybe your job is to complete a one-to-one refurbishment of an existing installation. Maybe you’ve been tasked with a new project. Or maybe what you’re doing lies somewhere in between those two poles. Each option will present its own logistical challenges. You might find, for example, that a supposedly one-to-one refurbishment isn’t as easy as it looks given that new luminaires can’t be inserted into the spaces the old ones occupied. Alternatively, local rules might make one-to-one replacement with superior modern equipment difficult or impossible. (See “Know your local standards,” above.)
 

Then there’s the matter of the lighting control system. Is there an existing one that you can put to use? If all you’ve got to do is provide new luminaires, your job might seem easier at first sight, but it could also create new challenges for your project. Maintaining the existing control system could prevent you from taking full advantage of the new LED technology. A completely new control system could be advisable from the point of view of optimizing luminaire quantity and power consumption as well as of delivering ideal lighting conditions and improved maintenance processes.

You’ll need to gather information about the characteristics of the tunnel before you start the work. What are its dimensions? How long is it?
 

You’ll also want to take into account its carriageway and walls. For example, certain types of asphalt will be more reflective than others, and that will play its part in dictating your lighting plan. The same goes for the tunnel walls. The light from your luminaires will bounce differently off white aluminium tunnel walls than it will off concrete – creating different challenges for drivers’ vision.

You’ll obviously need to know in which direction the traffic be moving through the tunnel, and how fast, and how many lanes the tunnel will contain, and how many vehicles are projected to use those lanes at what times.
 

Counter-beam or symmetrical/asymmetrical lighting point source luminaires like Philips TubePoint models will be the most appropriate light sources for a tunnel entrance zone. A wide range of lighting distribution products, such as those in the Philips Ledgine portfolio, will help optimize the lighting solution further, delivering the right amount of light at all times.
 

Calculating the access zone luminance L20 will also be key, so that you can ascertain the right level for the entrance zone. Keep in mind that the L20 value depends on the tunnel environment, but is independent from the tunnel luminaires. So you have to make sure that all designs for the same tunnel bore use the same L20.
 

In more interior tunnel zones, a linear lighting arrangement of the sort Philips TubeLine products lend themselves to, mounted either on the tunnel ceiling or on the cornice areas, is a good choice. Such an arrangement will ensure that you avoid strobe effects and deliver a higher comfort level to drivers.

With all of that information in hand, you can define what your installation will require, including the following parameters:
 

• Lth: luminance threshold, the luminance you need at the beginning of the tunnel, to avoid a black hole effect.
• L-int: the luminance you need in the tunnel’s interior zone.
• L-exit: the luminance at the tunnel’s exit. To ensure adequate direct illumination of small vehicles and sufficient rear vision via mirrors.
• L-wall: the luminance you need for the tunnel walls. Drivers should be aware of the walls, so that they have a clear background against which to distinguish obstacles.
• Emergency lighting levels: emergency lighting is generally part of the night-time lighting system, but is fed from an uninterruptible power supply.
• Uniformity ratio: this is country-dependent, but varies from 0.4 to 0.9. The objective is to ensure that there are no dark spots in the tunnel and that lighting is distributed equally across different surfaces.
• Glare rating: this is also country-dependent, varying between 6 percent and 20 percent. Because glare reduces visibility, it’s important to minimize it. Tunnel lighting professionals need to consider disability glare. Disability glare effects are quantified by Threshold Increment TI.
• Overall maintenance factor: maintenance of all lighting installations is essential, as it keeps the performance of the system within the design limits and promotes safety and the efficient use of energy. In the design phase, this maintenance is taken into account through the use of the overall maintenance factor (MF), which combines several different factors into one: MF = LMF x LLMF, with:
• Luminaire maintenance factor (LMF): dirt and dust can have a significant influence on the performance of a luminaire. The luminaire maintenance factor is a function of the installation’s cleaning schedule and the luminaire’s characteristics.
• Lamp lumen maintenance factor (LLMF): describes the light depreciation of a light source over the course of its lifetime. For LED-based luminaires, we have to consider the entire system, as the performance of the product is directly linked to product design via parameters like thermal management and electrical design. High-quality luminaires like Philips FlowStar and TubePoint provide very good LLMF values (above 0.9).
• Spacing restrictions: make sure that the spacing regime that governs the placement of luminaires is one that prevents distracting strobe effects.

Tunnels are designed for the brightest outside conditions. This stage of maximum brightness, however, is necessary only about 10 percent of the time. The rest of the time the entrance lighting level needs to be adjusted downward to different lighting stages, so as not to overlight the tunnel, which can result in consumption of too much power.
 

On the basis of the L20 portal luminance measurement, the tunnel’s control system will regulate its different lighting stages.
 

The number of stages has historically been defined as: sunny, bright, clouded, dusk/dawn. But today, using controls and connected LED lighting, it’s possible to add more stages and adjust the lighting to maximize the efficiency of the installation based on the conditions that exist outside. A control system like Philips BaseLogic, in concert with LED luminaires, can facilitate up to 12 different stages, improving the accuracy of your installation.
 

Philips TunneLogic control system, designed especially for LED lighting, can even provide for continuous dimming so that it corresponds exactly to the level of brightness outside. This complete tunnel lighting control and monitoring system lets you maximize visibility, safety and driver experience along the length of your tunnel.