Illuminated River
Illuminated River is a large-scale public art commission which lights up nine bridges in central London across the River Thames. Designed by American artist Leo Villareal in collaboration with British architects Lifschutz Davidson Sandilands, it uses LED light fittings to produce sequenced patterns of moving light across the bridge structures.

Illuminated River is a large-scale public art commission which lights up nine bridges in central London across the River Thames. Designed by American artist Leo Villareal in collaboration with British architects Lifschutz Davidson Sandilands, it uses LED light fittings to produce sequenced patterns of moving light across the bridge structures.
Check the official site before travelling; hours and prices can change.
More bridges

Tower Bridge
The bridge people mean when they say London Bridge. Walk the high-level walkway for the glass floor.

Millennium Bridge
Foot-only suspension bridge from St Paul's to Tate Modern — the only crossing aligned on St Paul's dome.

Hammersmith Bridge
Currently pedestrian-only, Victorian wrought-iron beauty — best photographed at golden hour.
Source: wiki-list