In Shakespeare's Macbeth, darkness vs light is one of the play's themes. This refers to the darkness that fights the light, thematically, in the play.
First, the witches set a tone of darkness in Act One, scene one. The witches are evil, and evil is associated with darkness. The light is seen in Duncan, a good and just King. When Macbeth kills Duncan, it seems for a time that darkness has won, and the light is lost.
The theme of darkness vs light is seen several times throughout the play. Lady Macbeth calls on the clouds to cover her in darkness so the stars cannot shed light on what she plans with the murder of Duncan. By the end of the play, she has lost her mind, is sleepwalking, and is trying to shed some light on her path with a candle, which must remain lit next to her bed all night long.
How came she by that light?
Why, it stood by her. She has light by her
continually; ’tis her command. (V.i.18-20)
Banquo is representative of light, but Macbeth also has him killed because Banquo suspects that Macbeth may have been involved with Duncan's death. Banquo is the only other person who heard the witches predict that Macbeth would be king.
After Duncan's death, there is a report of an eclipse taking place, in Act Two, scene four, so that darkness covers the light, a sign of unnatural occurrences. The following quote refers to darkness covering the sun.
...yet dark night strangles the travelling lamp.
It is not until Macduff, who is also a character surrounded by light, kills Macbeth, a character of great evil and darkness, that light reigns again. The opposites of darkness and light represent a battle between good vs evil. It is because Macbeth turns his back on the light and follows the darkness that he is destroyed in the end.