An Arclight is a spherical, magical and rare device that is used to entrap an Incubus, a metaphysical prison.. Olivia Durand describes it as "the most powerful weapon in the Caster world." According to Liv, Arclights are incredibly dangerous.
In order to trap the Incubus, the arclight must be physically touching them and a cast said. Additionally, to release the Incubus, a cast must be recited. Both casts are not recorded and are passed through the generations by word of mouth only. The Arclight flashed different colors when Ethan Wate, Liv, and Wesley Lincoln were getting closer.
Ethan Wate saw a memory of Macon Ravenwood giving the Arclight to Lila Jane Evers, not knowing what to make of the information at the time. It turned out when Macon was sacrificed to resurrect Ethan, he was actually saved by being trapped within the very same Arclight by Ethan's mom, thus Ethan and Liv were able to bring him back later on.
After Macon was resurrected, the characters hold a ceremony to bury the Arclight in Macon's gravesite (to prevent it from being used). Unbeknownst to Ethan, Macon and Lena Duchannes, Ridley Duchannes kept the Arclight knowing that John Breed had been enslaved within.
Cast to Imprison an Incubus
"Comprehende, Liga, Cruci Fige.
Capture Cage, and Crucify."
Freedom in Light Cast
"In Luce Caecae Caligines sunt, Et in Caliginibus, Lux. In Arcu imperium est, Et in imperio, Nox."
"In Illo qui Vinctus est, Libertas Patefacietur. Spirate denuo, Caligines. E Luce exi."
"In the One who is Bound
Freedom will be Found.
Live again, Darkness,
Come out of the Light."
- Arclights can be used to resurrect Incubuses. Incubuses who have Caster blood can be trapped in an Arclight, then released from it and become a Caster as seen with Macon.