This spell causes an object to radiate darkness out to a 20-foot radius. This darkness causes the illumination level in the area to drop one step, from bright light to normal light, from normal light to dim light, or from dim light to darkness. This spell has no effect in an area that is already dark.

This spell functions as darkness, except that objects radiate darkness in a 60-foot radius and the light level is lowered by two steps. Bright light becomes dim light and normal light becomes darkness. Areas of dim light and darkness become supernaturally dark. This functions like darkness, but even creatures with darkvision cannot see within the spell’s confines.

In response to the description, it depends on the darkness spell. Normal darkness bottoms out at “starless night.” Deeper darkness can create what’s called “magical darkness” that not even darkvision can see through. At least, that’s how it works in 3.5 and Pathfinder.