Greater Black Sky (3.5e Feat)
From D&D Wiki
 Greater Black Sky [Dark]
With experience you have learned to master the effectiveness of your black sky class feature.
Prerequisite: Darkness Class Feature, Black Sky Class Feature, Improved Black Sky feat, Dark Knight Level 20
Benefit: When you maintain the effects to create an area of darkness you now deal 1d4 per dark knight level of negative energy damage to all creatures in the area, excluding you.
Normal: When you maintain the black sky ability only an area of darkness is produced and no damage is dealt or only 1d4 per two dark knight levels of damage is dealt with the Improved Black Sky feat.