Since each post is separate and doesn't need to be done in real time I have a layer or two I use to show areas of bright or dim light. In the map below there is no dim light to speak of (dnd 4E bright light sources don't fade into dimness for simplicities sake I believe)
The darkness areas are not fully blacked out in this map as the characters have already seen the whole map but any creatures have been hidden. Until an area has been seen it would be totally black though I haven't been bothering to trim these maps for the delves. For other games I have cropped so players don't know the full size of the map when starting but it's often more work for no real point.