The power ring was an object issued to the members of the Green Lantern Corps.
Drawing on the power of the Guardians of the Universe, the power ring could theoretically do anything—its only limitations being the imagination and willpower of its wielder.
Frequently used capabilities of the power ring included: granting the wearer the ability to fly at tremendous speeds, even across interstellar distances; sustaining the wearer's life in hostile environments, including the vacuum of deep space; protecting the user from harm via a powerful force field aura; acting as an investigative tool for the wearer (such as detecting objects through walls, revealing pocket dimensions and homing in on other power rings) and, most familiarly, generating a beam which could be used for anything from simple offensive blasts to forming protective barriers or even more complex energy-constructs. It could also allow its user to phase through solid matter. An active force field could even passively protect those within from time distortions and changes in the timeline.
The power ring needed to be recharged once every twenty-four hours via the standard power battery.
Static's electromagnetic energy can act as an alternative energy source for the ring (though the energy generated has a more electric appearance). The ring's power was equally effective when charged this way, and Static could charge the ring while the bearer was using it. John Stewart used this method to defeat Sinestro after the rogue had stolen his power battery.
Other Power rings
The former Green Lantern Sinestro used a yellow power ring comparable to those used by the Corps. Details of its origin and power source remain obscure. Star Sapphire had a gem that worked like a power ring.
The Green Guardsman of the Justice Guild of America also possessed a power ring, which seemed to operate in an identical fashion to the Corps' rings but which was entirely useless against common aluminum. The energy generated was also opaque rather than translucent.