One of the main themes of imagery that runs throughout the play Macbeth is that of darkness. The play is full of dark and evil deeds. It is therefore highly appropriate that Shakespeare chose to set so much of the play in darkness. How was this possible in theatres during Shakespeare's time?
This is an important question. Remember that in the 17th century there was no such thing as electric or even gas light. The theatres were also mostly open-air. There were roofs over the stage and some of the seats, but a lot of the audience simply stood in the open air. There was none of the lighting and other special effects that are common in theatres today.
So Shakespeare had to create the dark atmosphere through words and images. He had to help the audience use their imagination to achieve that feeling.
Most of the important events in Macbeth take place in darkness:
The murder of King Duncan as he lies in his bed at night
The murder of Banquo takes place at night