Non-Damaging Ailments have 50% reduced Effect on you PoE

Non-Damaging Ailments have 50% reduced Effect on you while you have Arcane Surge

Illuminated Devotion is a ascendancy name for Hierophant. It grants:

• Non-Damaging Ailments have 50% reduced Effect on you while you have Arcane Surge
• 30% increased Area of Effect while you have Arcane Surge
• 0.5% of Spell Damage Leeched as Life while you have Arcane Surge

Guide

• Ailments that do not deal Damage are Scorched, Chilled, Frozen, Brittle, Shocked, and Sapped

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Are non-damaging ailments' effects based on the base damage of the inflicting hit or the total damage?

They are based on the damage actually taken by the enemy.