Standing in Poole, Dorset, England, the Twin Sails Bridge is the second road linking from Poole town center to Hamworthy. It is a lifting bridge which being designed in a pair of the sail-like triangular lifting leaves. Completed in April 2012, the bridge spans across the backwater channel in Holes Bay and the purpose is to connect four major sites together for vehicles. This is a project which began 30 years ago and Poole’s civic leaders believe their new Twin Sails Bridge is the key to regenerate the town. Lighting designers from Speirs + Major undertook the lighting design task and encountered challenges -- how to use light to encourage people to engage with the structure after dark, how to create a beautiful civic feature both when the bridge is open and closed.

Illuminating

In its static position the bridge is an exquisitely detailed horizontal form that celebrates the connection of the sea, horizon and sky. Light accentuates the long span by highlighting the structural ribs and creates beautiful reflections in the water. Functional lighting for the road, cycle ways and pedestrian decks is fully integrated into the vehicle crash barriers and handrails, allowing the lit effect to take complete precedence. A wave-form art screen made of stainless steel bars separates the pedestrian deck from the roadway on the fixed sections of the bridge. This screen is illuminated by red LEDs to lend a soft glow to the pedestrian areas as well as adds an extra dimension to the reflections on the water.

When being closed, the diagonal joint on the bridge deck separates into “sails” -- two sail-like leaves. As darkness falls, the opening sets a dramatic lighting transformation in motion. In an animated sequence the white light of the pedestrian walkway begins to turn to red, starting from the top of the ‘sail’ and appearing to roll downwards, eventually immersing the pedestrians in red light. This animation heightens the anticipation of the opening, creating a spectacular event for bridge users to witness and participate in. The sails are lit in white with a stark contrast to the darker deck surface. The strong vertical emphasis of the open bridge is enhanced by the carbon fiber mast, which is capped with a glowing section of frosted acrylic containing white LEDs.

Technologies

There are many practical considerations involved in lighting a bridge. The lighting technologies and luminaires applied on this project were carefully chosen for each specific condition in consultation with the Harbour Master, using lenses and focusing to reduce spill and glare. Long life and easy maintenance were high priorities, with luminaires located in accessible positions above deck or below gratings. The under deck structural lights are designed so that they can be rotated up for maintenance and back into their original focused positions. The road lighting in particular is provided by specialist cold temperature fluorescent lamps to ensure no disruption to output during the winter months. The lighting is controlled by a combination of time clock and photocell, with a direct link to the mechanical operating system to ensure that the night-time animation is perfectly synchronised with the bridge opening.