Darkness. There is no zone of dim light in 4e.
This is a funky ruling.
Funky and, arguably, wrong.
Compendium said:
Darkness
Darkness prevails outside on a moonless night or in rooms with no light sources. Characters who have normal vision or low-light vision can’t see creatures or objects in darkness. Characters who have darkvision can see without penalty.
That's darkness -- outside on a moonless night or in rooms with no light sources.
The rules never say what the visibility is in rooms that -have- light sources (eg, the torches, sunrods, etc the party is carrying with them) outside the "bright light" zones of said sources. Now, dim light...
Compendium said:
Dim Light
This category includes the light provided by a candle or another dim light source, moonlight, indirect illumination (such as in a cave interior whose entrance is nearby or in a subterranean passageway that has narrow shafts extending to the surface), and the light cast by things such as phosphorescent
fungi. Characters who have normal vision can’t see well in dim light: Creatures in the area have concealment. Characters who have low-light vision or darkvision see normally in dim light.
... Indirect illumination. Like, say, the zone of bright light filling the center of a room.
By strict RAW, a room with a source of bright light has no darkness in it (except for one with only dim light sources with known radiuses, of course). Instead, my best interpretation is that anything that has LoS (or close enough; see indirect light) to a bright light source is filled with dim light.
The rules -don't- do the bright->dim fadeoff of 3rd ed. But nor do they say that areas immediately outside a zone of bright light are pitch black (nor does it make any sense to say so, except -sometimes- with magical light).