In addition to the two options in the first anwer, let me add one instance from the book that I think may be the one you are thinking about in this question. The one I am thinking of is from Chapter 28.
This is where Jem and Scout are heading home after the Halloween thing. They are about to get to the street and be able to see the light when they are attacked. They struggle with the attacker for a while.
After the struggle is over, Scout gets out to the street and sees someone carrying Jem off down the street. The man carries Jem to the Finch house.
Another example comes when Scout is being escorted home by Arthur Radley in the final chapter of To Kill a Mockingbird. It would be the last time she ever saw him. When
"I turned to go home... Street lights winked down the street all the way to the town. I had never seen our neighborhood from this angle.
She could see all of her neighbors' houses, but they were now somehow different. "The night faded" into daylight, and Scout reminisced about the past two years since she had met Dill.
The street lights were fuzzy from the fine rain that was falling... when I looked at the tip of my nose I could see the fine misty beads... what a thing to tell Jem tomorrow.
There are two situations in the book that I believe you could be talking about.
The first is in chapter 6 when the kids are watching Mr. Avery shoot an arc of liquid from his body off the side of the porch. It seems to have a distance of about 10 feet and this is amazing to the boys she is with, although she's not so sure what the big deal is.
The second option I am thinking of occurs in chapter 15. The kids sneak to follow Atticus into town at 10 o'clock at night. Atticus is sitting under the light reading a newspaper propped up in his office chair against the jail just below Tom Robinson's cell window.