Gravity globe
From Tardis Wiki, the free Doctor Who reference
File:Maze-of-the-dead 02.jpg
A grav globe at work
A gravity or grav globe was a Human device to provide massive illumination. It could be sent aloft under its own power such that it would "hang" at a certain height and provide downlight over a large area. Grav globes were particularly useful in large caves. (DW: The Impossible Planet, The Satan Pit, The Time of Angels, Flesh and Stone)
