Tower Bridge has had a new lighting system installed ahead of the Queen's Diamond Jubilee and Olympic Games.
The lights are said to enhance the bridge's architectural features and replace static lights with bulbs that can vary in intensity and colour.
The world-famous central London bridge over the Thames will gleam white to celebrate the Queen's Diamond Jubilee this weekend.
The more energy-efficient lights will be switched on later.
Passers-by will see the system being tested in coming weeks to prepare for lighting displays planned for key moments of the Games.
The lights will highlight the giant Olympic Rings and Paralympic Agitos which will be fitted to the bridge featuring the Games.
In total 1,800 special energy-efficient LED lights have been fitted, along with 2,000 metres of energy-efficient LED linear lights, 5,000 metres of cable and 1,000 junction boxes.
London Mayor Boris Johnson said: "As London gears up for a summer like no other, this fantastic lighting make-over is another example of how the capital is benefiting from the Games.
"Tower Bridge can now play a starring role in our celebrations, starting off this weekend by being bathed in a stately white light for the Queen's Diamond Jubilee."
Mark Boleat, spokesman for the City of London Corporation, which is responsible for maintaining the bridge, said: "The new lights will give Tower Bridge an elegant night-time look for the next 25 years, with the capability of creating firework-like displays on occasions of importance for London and the nation."