As part of the Tokyo Hotaru Festival 2012, organisers lit up the Sumida River in Tokyo, with 100,000 solar-powered LED lights, which floated down the river.
The festival is inspired by the Japanese tradition of watching fireflies along waterways. Those taking part in the festival bought LED bulbs, which were then thrown into the river and eventually collected downstream using nets.
The LEDs passed by Tokyo Sky Tree, which at 634m is the second tallest structure in the world after Burj Khalifa.
The organisers have not specified what happened to the bulbs after the event.