Tailor-made solution for world’s 5th longest suspension bridge

Lisbon’s Ponte 25 de Abril is the fifth longest suspension bridge in the world and the biggest outside the USA. It poses a huge maintenance and illumination challenge because of the intense road traffic.


Ponte de 25 Abril, one of the world's largest suspention bridges.

With about 300,000 users crossing it every day, the maintenance has to be planned so as not to cause even the slightest bottle-neck or reduction in road safety. The lights are exposed to severe conditions such as wind vibration, passing trains, loads from road vehicles (the worst) and the flexing of the actual bridge itself. These extra challenges mean the lamps have a short life-span (weeks), cables, bulbs, ballasts, gear trays and light fittings come loose and there is material fatigue.

From this starting point, Aura Light offered Lusoponte, the company responsible for concession and maintenance, an energy-efficient solution that would reduce operating and electricity costs without compromising road safety for the drivers. This solution obviously also had to be financially sustainable. The bridge was illuminated by luminaires that were in an excellent state of repair, fitted with 250 W high-pressure sodium vapour bulbs and electric accessories, which Lusoponte said they wanted to keep if a sustainable solution could be found for doing so.

Durability and resistance against intense vibrations

Taking into consideration the roadway usage conditions, speed, traffic density, lane geometry and traffic reduction in the early hours of the day, Aura Light proposed a solution using Ecolum double level, stand-alone high frequency (60 Hz) electronic ballasts and Aura Sodinette Long Life bulbs with a guaranteed service life of 48,000 hours.

A pilot project was installed at 6 light points for 2 months and surpassed the highest expectations. However, when they moved on to install the lights on the entire bridge after those first 2 months, they saw a failure rate of more than 20%. When they investigated the damaged material removed from the bridge, the suspicions were confirmed: the bridge vibrations had simply destroyed the electronic ballast, turning it into a box of loose components.

Tailor-made solution

“With the experience and help of the Lusoponte maintenance department which sent us an in-depth study of 3-dimensional vibration amplitudes over the day, and our own R&D department, we succeeded in resolving the problem by finding a solution that involved strengthening the ballast component attachment and by replacing its fixing to the light fitting gear tray, the latter developed by Lusoponte.”

The savings speak for themselves

The solution has been installed for almost a year and has brought power savings of 40%, along with lower operating costs as a result of fewer interventions and a significant improvement in the illumination of the road deck.


Ponte 25 de Abril solution: