100,000 LED Lights,

were placed in the Sumida River, 

 n Tokyo, to resemble the fireflies that once inhabited it,

 powered by 100% solar power, the beautiful display kicked off the summer festival,

 For the inaugural Tokyo Hotaru Festival, made to resemble hotaru (fireflies), that once floated down the Sumida River through central Tokyo,

 dubbed “prayer stars,” the LEDs were provided by Panasonic, who claims that the balls, which were designed to light up upon contact with water, 

 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, sadly fireflies no longer inhabit the area, but there are other places to see these fascinating insects.