PBS | 9:00 pm

One reason fireflies on a summer night seem so magical is that few other land life forms can light up as these can. That’s business as usual, however, in the ocean depths, where nearly 90 percent of all species glow from within. "Creatures of Light" shows how scientists are examining how such animals use their ability to shine, whether it’s to attract a mate, repel predators or lure prey. Researchers also are finding ways to use this trait medically.