100,000 LED Balls Floating Down a River in Japan

As part of the recent Tokyo Hotaru Festival, 100,000 illuminated blue LEDs were released in the Sumida River. The impressive installation was made to resemble fireflies (hotaru) and looked like a blur on the river when viewed from a distance.

The spheres were 100% powered by solar energy and lighted up upon contact with water. For those of you worried about pollution or safety, the lights were later caught downstream by giant nets.