Last May 4, 2012 celebrated the inaugural of Tokyo Hotaru Festival which they displayed this fantastic LED Lights - made to resemble hotaru (fireflies), floating from Sumida River through Central Tokyo. These impressive presentation, consists of 100,000 LED Lights provided by Panasonic, which is 100% powered by solar-energy, and designed to light-up upon contact in water. After illuminating the whole stretch of the river, which also hosts a popular fireworks festival in the summer, the LEDs are caught in the large net.
There are plenty of literary references indicating that 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 that time) during the 18th century. For said and obvious reasons, fireflies no longer inhabit the area. The Tokyo Hotaru Festival is part of the city's "Sumida River Renaissance" initiative.