The significance of Lee using light and dark is symbolic. Light and dark can refer to skin colors; they can also refer to literal light and literal darkness.
Tom is all alone in the dark jail in the dark night. His future also look dark to him. This is the perfect time for the mob to attack Tom--they won't be seen. The mob can also be seen as symbolically representing darkness--ignorance.
Atticus bring the light--literally and figuratively. Atticus hooks up a light bulb so he can read in front of Tom's jail cell and protect him. Atticus is also trying to do the right things, and spread the "light"--the knowledge of equal rights and the humanity of the black people to the others in Maycomb.
Light and dark usually symbolizes good and evil and in this case that is what Harper Lee intended. Chapter 15 is the first fight between good and evil. The group of men who come to the Finch house in the evening are there to persuade Atticus to have Tom Robinson held somewhere besides Maycomb. They come under the cover of darkness because, in the light, their requisition would appear irrational. The darkness seems to cover the fact that they should be outstanding citizens and friends of the Finch’s. Their actions prove otherwise when they threaten Atticus by telling him he has “everything to lose from this” (Lee, Ch. 15).
Later that night when Atticus goes to sit watch over Tom Robinson in the jail, he brings along a single lamp. The lamp seems to symbolize what is just, and the fact that Atticus is in possession of the lamp tells the reader that he is the one trying to shed light on the fact that prejudices are wrong.
The thing about Atticus standing under the light in the jail house; represent justice, and a whole exposition of truth about robinson's issue.The thing is,when those people had an intention of going to the prison to kill Robinson, they disguised themselves.They hid the whole truth about their identity.
for example when jem was in the dark he was scard thinking attcus might get jumped vut recklessly said the phone was ringing out loud not knowing was happenong
I think the symbloism about light and dark i really think it means really in action that happen in the light and dark