Four London bridges have been illuminated in what is the first phase of a £45m project to create the longest artwork in the world.

London, Cannon Street, Southwark and Millennium bridges had their municipal lighting replaced with dynamic – possibly soothing – LED displays created by the US artist Leo Villareal.

Next year another five will be lit up, followed, it is hoped, by the remaining six, creating the Illuminated River project – 4.5 nautical miles (almost 5.2 miles) from Tower Bridge to Albert Bridge – the longest public art commission in the world.

London bridge and Cannon street railway bridge are illuminated in the first phase of the project. Photograph: Chris J Ratcliffe/Getty Images

The scheme, funded by wealthy patrons, is about bringing beauty to places where it is hard to find. Hannah Rothschild, who originated the project, said the Thames was London’s beating heart and the bridges connecting arteries.

“But at night these extraordinary structures, each with a unique history and style, evanesce into darkness and obscurity,” she added.

Rothschild added that the idea was to “transform a snake of darkness into a ribbon of light, threading art through the heart of the city”.

Cannon Street Bridge.

May 2019 Photograph: James Newton

The project was announced in December 2016 and has been much trickier and taken longer to realise than anticipated.

“We had to do 30 planning applications, 18 listed building consents, deal with five bridge owners and seven local authorities,” said the project’s director, Sarah Gaventa. “It has been quite a protracted process.

“The worst place you can ever install anything is over a working river. We needed abseilers with electrical engineering degrees and we ran out of them … we had to get more from Germany.”

Then there were bats, birds and fish to worry about, all the subject of lengthy studies and meetings to discuss the possible impact.

On fish, Gaventa said the project would be better for the 135 different species in the Thames because it would not spill light directly on to the water. “Fish don’t like having sex with the lights on.”

The team also took great pride from the security camera it set up under Cannon Street Bridge to ensure a nesting Egyptian goose and its subsequent offspring were undisturbed by contractors.

Cannon Street Bridge. Photograph: James Newton

Villareal is best known for lighting up San Francisco Bay Bridge and has worked on the project with the British architectural practice Lifschutz Davidson Sandilands. He said he had spent three years, “a fantastic experience”, studying the river and the history of London and was inspired by artists who have painted famous Thames scenes including Monet, Whistler and Turner.

Backers say the illuminated bridge project is not a light show. “The light plays across the bridges,” said Gaventa. “It is slightly kinetic, slightly moving, but not fast, this is not disco lights. At the end of the day we want people to pause, have a moment.”

The Millennium Bridge. Photograph: James Newton

The lights, which replace schemes mostly designed by highways engineers, will be switched off at 2am to allay concerns about light pollution.

The main money for the project has come from the Rothschild Foundation, the Blavatnik Foundation and Arcadia Fund, the charitable fund of Lisbet Rausing and Peter Baldwin. Seed funding for the initial competition came from the mayor of London and money to replace light fittings on London Bridge came from the City of London corporation.

Each bridge will also have pieces of its own music, commissioned from the Guildhall school of music

It will cost roughly £3m for each bridge and the Illuminated River project team will fund and maintain it for 10 years. “The lighting kit can last for 20 years and then I think it’s up to the public and the media to decide what next,” said Gaventa.