While firing, Void Rays can calibrate their emitters and gradually increase attack damage during combat. Every 4 seconds while stationary, they get x1.01 damage multiplier, which persists until the end of combat. Maximum damage bonus is limited at 70 stacks of multiplier (about 100% increase).
If there are allied human Destroyers with active Battle command ability, multipliers of both abilities will combine and stack to the same limit (100%), but it can be reached faster.