Dark - Curleys Wife
When Curley's Wife enters the Bunkhouse;
"the rectangle of sunshine in the doorway was cut off. A girl stood there"
Curley's Wife blocks out the chance/hope of George and Lennie's dream, and stops light reaching George and Lennie.
Light and Dark - The Bunkhouse
In the Bunkhouse at the beginning of Chapter 3;
"Although there was an evening brightness showing through the windows of the bunkhouse, inside it was dusk."
The light tries to get into the bunkhouse, but it never manages to penetrate the darkness.
The Bunkhouse symbolises isolation, blocking out the dream. The brightness remains outside.
Dark - Crooks' Eyes
Crooks' eyes symbolise darkness when we meet him in the novel, but also have a slight air of light in them.
"lay deep in his head, and because of their depth seemed to glitter with intensity"
There is an air of mystery with Crooks. The depth of his eyes suggest darkness, as he has very little/no hope. "Glittering with intensity" suggests that there is some light, he has a dream and an opinion.
Dark - Crooks' Room
Crooks room offers very little light;
"In the stable buck's room a small electric globe threw a megre yellow light"
Symbolically, the light shows that Crooks has very little hope but mainly darkness and no chance of achieving a dream.
Light - Prior to Curleys Wife's Death
Just before Curleys Wife dies;
"the sun streaks climbed up the wall"
Element of a soul/spirit leaving, preparing for death. Acheives a natural death, return of innocence. Light climbing towards freedom.
Light - After Curleys Wife's Death
After Curleys Wife dies;
"the sun streaks were high on the wall now, and the light was growing soft in the barn"
The light hasn't filled the barn, but there is no real darkness to create doom and panic. The sun streaks could represent a soul leaving, freedom and innocence. Light symbolises dream, and the light being high on the wall symbolises the impossibility to reach it.
Dark - Lennies Death
As the story reached its tragic conclusion;
"The light climbed out of the valley"
After Lennies death, the light goes and symbolises the loss of companionship and the dream. Tragedy and inevitable death are shown here.
Dark - Lennies Captors
As Lennies captors advance;
"Already the sun had left the valley to go climbing up the slopes of the Gabilan Mountains, and the hill tops were rosy in the sun"
Away from the ranch, and the scene is back in nature. The light is personified, and symbolises the end of the dream and hope.