In Chapter Nine of Mark Twain's The Adventures of Huckleberry Finn, Huck and Jim have left the high end of island in their canoe, and before them they see a two-story house drifting down the Mississippi River. For Huck and Jim, the house represents the potential for supplies. The two climb "aboard," even while the "frame-house" is titled radically to one side. They enter in through a window on the second floor, but it is too dark to see. So Jim and Huck tie the canoe to the house and wait for the daylight to appear with dawn. Finally, light comes up over the horizon.
The light begun to come before we got to the foot of the island. Then we looked in at the window.
This statement means that the sun is beginning to rise before the house approaches the end of their island. With the sunrise, there is now enough light so they can look inside the window to see if there is anything inside that they can use. The quote, "The light begun to come..." is referring to the sun coming up.