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Thorn created a tailored LED lighting solution for this major undersea tunnel


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  • Lamp efficacy

    Lamp efficacy

    Ensuring the lamp efficiently converts electricity into light (lm/W).

  • Ballast classification

    Ballast classification

    Controlling the electricity supply to the lamp (Energy Efficiency Index).

  • Luminaire distribution

    Luminaire distribution

    Controlling light emission using optics which bend and shape the light to the correct location.

  • System efficacy

    System efficacy

    Combining optical and thermal control within the luminaire (luminaire lm/W).

  • Presence/absence detection

    Presence/absence detection

    Presence: Lights automatically turn on/off with movement. Absence: Lights automatically turn off and must be manually switched on.

  • Daylight detection

    Daylight detection

    Artificial lighting which responds to the natural light conditions.

  • Constant illuminance

    Constant illuminance

    A function designed to produce correct light levels for the duration of the maintenance period.

  • Task-scene setting

    Task-scene setting

    Allowing the user to set scenes and adapt the lighting to different tasks.

  • Timed off

    Timed off

    Automatic cut-off can be installed to turn all lights off during unoccupied hours.

  • Task lighting

    Task lighting

    Lighting task areas with the correct amount of light.

  • Zoning of lighting

    Zoning of lighting

    Lighting is zoned according to area use.

  • Maintenance schedule

    Maintenance schedule

    Maintenance must be performed in response to product age, performance and environment.

  • Waste light

    Waste light

    Eliminating waste light which does not hit the intended target.

  • Reflectance


    Taking advantage of light which is reflected from the surface within the space.

  • Visible smart metering

    Visible smart metering

    Results of actions can be quickly seen as increased or decreased energy use to encourage responsible energy consumption.


Thorn has provided a customised LED lighting solution for the Eurasia Tunnel in Istanbul – the only tunnel in the world to link two continents.

Opened in December 2016, the 5.4km tunnel carries 120,000 vehicles a day under the Bosphorus strait, between the European and Asian sides of the Turkish capital.

It was built by a partnership of Turkey’s Yapi Merkezi and South Korea’s SK E&C, who will also operate the tunnel for the next 24 years.

Lighting objectives

When the project to build the €1.2 billion tunnel began, it was expected to be lit by traditional HID (high-intensity discharge) lighting. But with rapid advances in the output, control, lifetime and cost of LED lighting, the client decided to go for an LED solution.

The tunnel’s double-deck construction intended for small vehicles only means its ceiling height is relatively low, so achieving the right light distribution was particularly challenging. The client, who will be operating the tunnel for the next three decades, also set down extremely demanding standards for durability, ease of maintenance and budget.

Thorn worked with its longstanding Turkish partner Kitoko to come up with a tailored solution.

Lighting solution

Thorn’s GTLED PRO tunnel luminaire was already in development when the company began working on its proposal for the Eurasia Tunnel. Thorn technical manager Hans Øien says: “When we showed the GTLED PRO concept to the end user in Istanbul, they really liked it, so we kept developing it with this project very much in mind.”

Of the twelve lighting suppliers that initially bid for the project, Thorn was one of just three to be shortlisted. These three were then invited to light a 100-metre section of the tunnel as a mock-up.

Thorn came up with a customised combination of lenses and optics, achieving the optimal light distribution for the shape of the tunnel. As a result, Thorn’s solution met the project’s technical requirements with much wider spacing between luminaires than the two competitors: 9 metres which gave a clear advantage.

Wider spacings means fewer luminaires; approximately 900 pcs in this case, lower equipment costs and less maintenance – and this was a key factor that led Thorn to win the project.

Thorn’s production plant at Les Andelys in France then had to deliver 3,500 customized luminaires in the space span of a few months, dedicating around half the plant’s capacity to the project and making significant investments in additional production equipment.

Achieving the correct light distribution was one of the biggest challenges, says Hans Øien. “There were very strict requirements when it came to uniformity, light comfort and glare. We had a lot of different optics available, so we tried out various combinations of different lenses and eventually came up with something that hadn’t been done before, that gave us the perfect light distribution for the geometry of this particular tunnel.”

Ali Ekrem of Kitoko, Thorn’s partner in Turkey, said: “This was an investment project for the client and their technical criteria were a lot stricter than on a standard contractor project. They went way beyond typical international specification, and all our product tests and calculations were reviewed very thoroughly. They really wanted the best of the best on many points: performance, cost, technical requirements, installation, ease of maintenance, guarantee, energy consumption… Every kind of lighting challenge you can think of was there on this project.”

Results and benefits

“The choice of manufacturer was made based on Thorn’s advanced technology and high-performance products,” Because of the demanding security and performance criteria, Thorn made a special lighting fixture for this tunnel. The suitability of the luminaires for the standards has been checked and certified by independent international institutions,” says Nail Eren, Lighting Consultant.

Hans Øien says the solution for the Eurasia Tunnel has turned out just as intended.  “The results of our light calculations have all been verified, which shows that our original design was very accurate. The uniformity is excellent, glare is very low, and we managed to light the entrance zone of the tunnel with only two rows of light at 360cd/m2 and a maintenance factor of 0.68, which is a real achievement.”

The DALI-enabled luminaires can be easily controlled to dim up and down in response to light levels outside, to ensure that drivers’ eyes can adapt as quickly as possible as they enter and exit the tunnel, and at the same time minimize overlighting and reduce energy consumption.

The luminaires are guaranteed for five years, and are expected to operate for more than 100.000 hrs or up to 25 years before needing maintenance. Because the light output of LEDs declines gradually over time, the control system has been programmed to compensate for this, to keep light levels constant. This means they are currently running at about 30% power, and will gradually adjust up to more power as needed. This means they are currently running at less than full power, and can gradually move up to full power over 10 years.

Thorn is already looking at other tunnels where the new GTLED PRO luminaire can be customised to offer the ideal solution. Already the product is being installed in several tunnels in Norway and Austria, with many more in the pipeline, where this generation of GTLED will offer even better performance at a lower price. Thorn has the experience and skillset required for such projects, with 50+ tunnels making use of the previous generation GTLED and numerous projects with the conventional Gotthard range that has been on the market for more than 30 years.

Product: GTLED PRO

GTLED PRO is an advanced linear shaped LED tunnel luminaire, which provides comfortable lighting with disability glare (TI) values of 6 or less in most applications, and thanks to its large luminous areas also minimal discomfort glare. Lenses provide tunnel-specific light distributions for road luminance levels from 0.5 cd/m² for the interior zone, and up to 400 cd/m² for the entrance zone, in many cases using only a single luminaire row. GTLED can cope with ambient temperatures up to 50°C and is rated IP66. Along with advanced and innovative controls – including self-addressing luminaires, CIE88 compliant Lseq or L20 cameras at the entrance, Lint cameras for actual interior luminance surveillance, making use of actual velocity and traffic volume data, Thorn can tailor a perfect solution for each and every tunnel project.