First 100 meters of the RijnlandRoute tunnel in The Netherlands will be illuminated with the natural sunshine. That is thanks to the optical fiber technology to be used in the tunnel. The optical fiber cables will capture the sunlight outside the tunnel and carry it up to 100 meters without any loss of light.

When cars enter the tunnels, it is important that the first 100 meters be illuminated because drivers are coming from sunlight and their eyes need adaption to the tunnel. Therefore the tunnel entries are always illuminated. It is the first time that, that illumination will be done via sunlight, at least during the daytime.

According to Dutch construction news site Cobouw, the optical fibers will provide between the 10-20% of total energy consumption in the tunnels. That is a lot of free energy. It is also important for the consortium building the Rijnlandtunnel as it is responsible for paying the energy bill for the 15 years long DBM contract.

492 million euro Rijnlandroute tunnel is built by the Comol5 consortium comprised of Mobilis, Croonwolter & Dros, Vinci and Dimco. 

https://www.cobouw.nl/infra/nieuws/2020/01/via-glasvezel-schijnt-zonlicht-100-meter-in-tunnel-rijnlandroute-101281282

image credit: By BigRiz Wikipedia, CC BY-SA 3.0