Light fantastic

15 April 2008

The 100 tonne capacity all terrain crane with 52 m main boom and 10.8 m jib made it possible for Sky

The 100 tonne capacity all terrain crane with 52 m main boom and 10.8 m jib made it possible for Skylight to make a spectacular 'full fire sun' multicolour light show to illuminate the 80 m building f

The annual Festival of Light in Lyon, France, is a 150-year old tradition that has evolved from a reli he annual Festival of Light in Lyon, France, gious celebration to a majorTevent. Spectacular lighting displays attract more than four million visitors to the city every year The event, which runs for four days in early December, features more and more ambitious lighting installations in different parts of the city, spotlighting more than 20 main sites and monuments.

For the 2006 f estival French events management company Skylight was selected to illuminate the Hotel du Dé partement in the centre of the city, which immediately threw up a number of challenges. The Skylight ideas – to create a sus pended chandelier effect over 40 m above the ground, lighting an 80 m square facade area of the 19th century building–required a crane able to hold 3 tonnes of lights at a specific angle, as well as to accommodate two large and heavy electric power supply cables.

To light the antique facade, as the sun does, every day, with moving colours from morning to evening, with moving shadows,”explains Jean-Marie Leriche at Skylight. It was a 20 minute “concert of light”set to the music of Mozart and performed between 6 and midnight.

“To bring such a project to completion was a considerable problem. The source of the light had to be suspended at a height of about 50 m above the ground to take into account the angles that we had calculated. Thus we thought of hanging a monumentalhigh-tech chandelier in the sky – t hree tonnes held in space on the boom of a crane”.

The project was further complicated by the proportions of the building. Only one crane was found able, due to its dimensions, to get through the entrance to the building – it was a 100 tonne Liebherr all terrain. “A nd we chose Mediaco Rhone Alpes because they were the only one that could provide the crane, thanks to their large local crane stock.

“The main hanging cable design was such that at each telescopic section the cable was strapped without any stress. The cable was retained by the strap, each telescopic section holds 10 m of 125 Amp and 63 Amp cables, so the whole cable weight is divided by the five telescopic sections to avoid any risk of stretching,”Leriche explains.

The lighting rig was a 7.5 m diameter Alcatruss hoop with a 600 mm triangular section and suspension points. “To raise the 3 tonne chandelier, the whole telescopic jib was in place in the sky. The hook took the chandelier truss with four chains and the chandelier was lifted up from the ground to the upper jib location,”Leriche says.

To complicate the operation, the lighting rig had to be hoisted up every day before the show and let down every night with the power still live and the light projectors still attached.

“With such an artificial electric sun system, we were obliged to use a strong circular lightweight truss and put 12 xenon sun-lite projectors [5,000 W]. And to hang that, a giant crane was the only safe solution. With a 100 tonne jib, it was possible to play with the lights over the roof. This was our concept artistic challenge, that we achieved, thanks to the crane,”Leriche concludes.

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