How does the boys' meeting place look different later in the day in Lord of the Flies?

With the change of the light because it is at the end of the day, Ralph notices that the sun slants in at one side "so that the shadows were where they ought to be."  Before, when the boys met earlier in the day the green roof was

lit by a tangle of golden reflctions, and their faces were lit upside down--like, thought Ralph, when you hold an electric torch in your hands.

The reality of the scene causes Ralph to fall "into that strange mood of speculation that was so foreign to him."  Ralph begins to ponder existence and its meaning.  He asks himself, "What was a face?  What was anything?"  The ambiguity of what is real sets upon Ralph, and he has "to adjust his values."  Also, the sun in his eyes causes Ralph to realize that time passes, so he takes down the conch, pondering how Piggy can think so much better than he.  With the more realistic slant of light, the noble, but inadequate leadership of Ralph comes fully and realistically into view, and the meeting goes badly as Jack asserts himself and convinces the boys of his perspective on the beast.

As the evening comes, one little boy tells of his horrifying experience one night when he saw things; Simon stands up to admit that he had been out at night, and Ralph looks at him, astonished.  But, Simon replies that he wished to go to a place that he is comfortable, but he becomes inarticulate, unable to communicate what he knows of the "beast."  Just then "two grey trunks rubbed each other with an evil speaking that no aone had noticed by day.

With oncoming night, the reality of their surroundings change, as do the reality of what is happening.  In the darkness, evil more easily emerges, and Simon "stirred in the darkness."  The meeting ends with Ralph wishing that someone could send them "something grownup."  Then "a thin wail out of the darkness chilled them"; little Percival was experiencing something horrible.

Clearly, Golding's use of light/dark imagery is meant to throw shadows of doubt onto Ralph, and to reveal more of the evil that lies in the hearts of man.