Deepen Shadows

Over the course of a minute, the shadows in a 10-foot cube grow larger, deeper and more concealing, causing a brightly-lit area to become dimly-lit and a dimly-lit area to become dark. The change is so gradual that it requires a Wisdom (Perception) check, using your spell save DC, to notice it while it is occuring. Any light-based magic will end this spell.

At Higher Levels. The size of the area that can be affected increases when you reach 5th level (20-foot cube), 11th level (40-foot level) and 17th level (80-foot cube).