In 2010 Tokyo, Japan opened their first Tokyo Hotaru festival which is a part of the city’s “Sumida River Renaissance” initiative. Kicking off the festivities were an impressive display of 100,000 LED lights – made to resemble hotaru (fireflies) – that floated down the Sumida River through central Tokyo. Dubbed “prayer stars,” the LEDs were provided especially for the event by Panasonic, who claims that the balls, which were designed to light up upon contact with water, were 100% powered by solar energy. After illuminating a large stretch of the river, which also hosts a popular fireworks festival in the summer, the LEDs were all caught in a large net.
There are plenty of literary references indicating that the Sumida River was once home to real fireflies, which were said to gather around clean, running water. Searching for these luminous creatures on the banks was a popular activity in Tokyo (Edo, at the time) during the 18th century. For sad and obvious reasons, fireflies no longer inhabit the area.