LONDON — London’s bridges will slowly fill with light as the tide rises. Luminous colors will wash across their surfaces. Beams will shoot out from each bridge, pierce the sky and then drop, connecting with a beam on a neighboring bridge to trace the path of the Thames. The bridges’s underbellies will glow gently; the banks will offer floating stages for performances; waterfalls will create a screen for projections; a weave of projected light planes will hover over the surface of the Thames, creating a ghostly river of light.

These are some of the ideas put forward for what is being called the largest-scale permanent public art project that any city has yet undertaken. “Illuminated River” is a hugely ambitious, £20 million ($24.8 million) plan to light the span of the Thames River from the Albert Bridge in the west to Tower Bridge in the east. (The money will come from private and philanthropic sources, with $12.6 million already contributed by the Rothschild and the Arcadia foundations.) It aims to transform this part of the Thames into a glowing river of light and spectacle, and is part of the city’s ambition to match other international metropoles with a vibrant nighttime economy.

The light project will also draw tourists to the bridges and banks of the Thames, which traces a loose S shape through central London, and has 17 bridges along its trajectory. The river is now “a black snake” through the city at night, Hannah Rothschild, the chairwoman of the Illuminated River Foundation, said at a preview on Monday of a three-week exhibition of the final proposals. With this project, she added, the transformation will be dramatic: “Light, energy, beauty, commerce, at the flick of a switch,” she said, adding that it was also a meeting point for art, design and technology.

The six finalists were chosen from 105 entries, including big-name architects, designers, engineers and artists of all stripes from all over the world. The winning team will be announced on Dec. 8, and the organizers hope that the project will be started by 2018.