Walk south from St Paul’s Cathedral, itself gloriously lit but merely corroborating what we already know and admire of it, over the Millennium Bridge and east along the south bank of the Thames to see the revelatory sequence of Southwark, Cannon Street and London Bridges. Formerly either blanked out by nightfall or dully picked up in a single wash of yellow or blue, they now unpeel in front of your eyes along the riverbank, linked by their calibrated tones and shifting timing, subtle painterly effects achieved by LEDs and computer programming.