Surge of Light

Surge of Light is a priest talent that grants a 3/6% chance when casting Smite, Heal, Flash Heal, Binding Heal or Greater Heal to cause your next Flash Heal to be instant cast and cost no mana.

Tips and tactics
In situations where mana is tight, Surge of Light can be used as often as possible, conserving mana that would otherwise have been spent on healing. By reducing mana consumption, SoL can reduce the priest's (and often therefore the group's) downtime, due to a reduced need for mana breaks. When soloing – provided Smite is being regularly used – Surge of Light can often provide all healing required by the priest, so conserving mana for offensive spells, as well as reducing downtime.

In PvP, Surge of Light can be very useful due to its instant cast capability, offering emergency burst healing and preventing interrupt effects.

However, as Surge of Light doesn't increase Flash Heal's healing per second (HPS), it is not always advisable to consume the buff immediately. Particularly in high-pressure situations where healing throughput is more important than efficiency, it may be better to prioritize abilities with higher HPS over SoL-boosted Flash Heal. This is most apparent in situations where multi-target healing is desired, as Flash Heal can only heal a single target, but can also affect single-target healing. Its 10 sec duration allows for a few heals to be cast in-between without losing the buff entirely.

Those concerned with their overall HPS may wish to examine the contribution of these free heals and balance them against their other options.