The Mind Blast does additional damage to players based on their current Meditation Penalty from armor. The spell also does additional damage to creatures based on their armor value.
The damage bonus to Players is (Total Meditation Penalty % / 2)
The damage bonus to Creatures is (.25% * Total Armor Value)
So against a player wearing full plate (which has a 100% Total Meditation Penalty) the Mind Blast spell would inflict +50% damage. Against a creature with an Armor Rating of 100, the Mind Blast spell would inflict +25% damage.