Umbral Spell (4e Feat)
From D&D Wiki
Umbral Spell [Metamagic]
Your spells are as dark as the darkest night.
Prerequisite: 11th Level, Wis 15, Wizard
Benefit: When you use a burst or blast wizard attack spell, you can choose to take a -2 penalty to add the following effect: The power gains the necrotic keyword. Squares of a zone with the radiant keyword that fall under the burst or blast are dispelled, and all light sources within that area of effect are extinguished.