Beginning at 6:30 PM last Sunday night, 100,000 glowing blue orbs were poured into Tokyo’s Sumida River as part of the Tokyo Hotaru (firefly) Festival. The display was part of an art installation named Hikari no Symphony (symphony of light) that included the lighting of Tokyo’s new Sky Tree tower and a musical performance form singer-songwriter Kaori Mochida.
While the Sky Tree was lit up, the big unveiling of the world's tallest tower isn't scheduled until May 22nd. This kind of river-lighting display isn’t unique by any means — there are similar events all over the country, often coinciding with Tanabata festivals in July and August. That said, the Sumida River glowing blue with the Sky Tree lit up in the background is a particularly special sight (as you can see in the video from YouTube user stevenagata below).
For the event, Panasonic created a special kind of orb called an "Inoriboshi" (prayer star) that incorporates one of the company’s HIT photovoltaic cells, a rechargeable battery, and an LED chip. A sensor on the orb’s bottom causes it to light up when it's placed in the water. Also, just to assuage any environmental concerns, all the orbs were collected with a net downriver so that they can be re-used.