In Macbeth, how does the nocturnal setting of Act 2, Scene 1 contribute to the scene's overall mood?

Considering that the second scene of Act II has an overall ominous mood, the nocturnal setting seems to fit perfectly.  It is the very scene before Duncan is killed; therefore, Macbeth is becoming all the more affected by his ambition.  It is also a night without the light of the moon as Fleance notes within the first few lines that "the moon is down."  All of the characters, then, must carry torches (as the stage directions dictate).  Throughout the scene it is most interesting to note the unnatural images in addition to those of both darkness and blood.  For example, Macbeth soon sees a bloody dagger hovering before him.  "Is this a dagger which I see before me, The handle toward my hand?"  In addition to the ominous ghost-dagger, Macbeth speaks of "dudgeon gouts of blood" and "the bloody business" and how "nature seems dead”:  all things that are out of the natural world, all greatly disturbing.  This scene is truly a good precursor to Macbeth's evil deed.