You can cast a spell such that it becomes invisible.
Benefit: Spells affected by this feat have no visual effects; spells based on light (such as prismatic spray) have no effect when modified by this feat. The spell is not magically silenced, and certain other conditions can render the spell detectable (such as destruction of objects or disturbing a puddle). A Perception check (DC 20) reveals what has happened. An invisible spell uses up a spell slot three levels higher than the spell’s actual level.