Halo sends out an expanding ring of Holy energy that damages enemies and heals allies it passes through, out to 40 yards.

It is Archon only. Holy Priest raids Archon, so in practice every raiding Holy Priest has it, but a priest on Oracle does not have the button at all.

Every Halo stacks Resonant Energy: 2% increased healing done per stack, up to 4 stacks, each lasting 10 seconds. It also feeds Surge of Light procs, so the ring is as much a ramp for the priest's next casts as it is a heal on its own.

On a 60-second cooldown it is mostly fired as it comes up, but it is worth a planned slot ahead of the priest's bigger windows. Line it up just before Apotheosis or Divine Hymn so the Resonant Energy stacks and Surge of Light procs are already running when the window opens.

Don't hold it longer than ~30 seconds, letting it drift costs noticeable healing throughput.