A gravity globe, or grav globe, was a human device to provide massive illumination. It could be sent aloft under its own power so that it would "hang" at a set height and provide light in a large space. Gravity globes were particularly useful in large dark caves.
Ida Scott used a globe to light up a cavern ten miles beneath Krop Tor's surface. (TV: The Impossible Planet / The Satan Pit)
The Eleventh Doctor used a globe to light up the Maze of the Dead. He later shot the globe to create an "updraft" to allow him and his group to escape into the inverted Artificial gravity field of the crashed Byzantium. (TV: The Time of Angels / Flesh and Stone).