At this point in the play, Amanda, Jim O'Connor and Tom are sitting around the table getting ready to have dinner. Amanda has worked very hard on the evening, spending extra money to make the apartment look good, making a special meal and just when she thinks that there is a chance that her mission might actually have a chance at being successful, the lights go out.
Amanda is embarrassed by the lights going out, she suspects that Tom has not paid the electric bill, so she covers her shame at being plunged into darkness by referencing Moses, a biblical figure, a leader and champion of the Jewish people who led them out of the darkness of Egyptian slavery into the promised land. It took 40 years of wandering. Amanda's reference is an attempt to minimize the negative effects of suddenly being plunged into darkness. She is, afterall, trying to impress Mr. O'Connor.
The Wingfields in darkness is both literal and figurative, Moses was both figuratively and literally in the dark as well. No, I don't think that there is a difference. Since the Wingfields will be in the darkness for a long time, just as Moses, they share a similar fate. Except, that Moses had the light of God to lead him, he never felt emotionally barren, or in emotional darkness. I think that the Wingfields do feel emotional abandonment because of Mr. Wingfield's absence from the home.
There is a darkness in Tom that has poisoned his view on life, simultaneously, Tom is both resentful and envious of his father for escaping the confines of the relationship with his mother.
Moses triumph came through perseverance and faith. Amanda is a survivor and has managed to raise her children alone after her husband abandoned her. This was a very difficult time for a woman to be alone, there were no government programs available, no food stamps, no welfare, no social security. Amanda is a hero for surviving and she draws strength from referencing Moses at this moment of literal darkness for her.