We are familiar with the obvious uses: The Light of knowledge or the Darkness of the Soul, but writers can use darkness and light in a myriad of ways!
Light or enlightenment can refer to:
understanding or knowledge: from the prosaic to the sublime
an attitude, emotion, or personality unencumbered with worries
Darkness can refer to:
ignorance, in all its many forms
an attitude, emotion, or personalty fraught with melancholy or ill will
tainted or impure thoughts
Light and dark symbolism can:
describe a character’s mood or personality
foreshadow a character’s intent
foreshadow an event
indicate a setting’s moral/ethical beliefs
provide (moral/ethical/religious) contrast between opposing characters/themes/events
be a plot device
be a symbol
be a theme
be a recurring motif
Here’s one of my favorite poems about “light.”
The Man Who Spilled Light, by David Wagoner
The man who spilled light wasn’t to much to blame for it.
He was in a hurry to bring it home to the city
Where, everyone said, there was too much darkness:
“Look at those shadows, they said. “They’re dangerous.
Who’s there? What’s that?” and crouching,
“Who are you?”
So he went and scraped up all the light he could find.
But it was too much to handle and started spilling:
Flakes and star-marks, shafts of it splitting
To ring-light and light gone slack or jagged,
Clouds folded inside out, whole pools
And hummocks and domes of light,
Egg-light light tied in knots or peeled in swatches,
Daylight as jumbled as jackstraws falling.
Then everything seemed perfectly obvious
Wherever they looked. There was nothing
they couldn’t see.
The corners and alleys all looked empty,
And no one could think of anything terrible
Except behind their backs, so the all lined up
With their backs to walls and felt perfectly fine.
And the man who’d spilled it felt fine for a while,
But then he noticed people squinting.
They should have been looking at everything,
Should have been perfectly clear, and everyone
Should have seemed perfectly brilliant, there was
Dazzle: people were dazzled, they were dazzling.
But they were squinting, trying to make darkness
All over again in the cracks between their eyelids.
So he swept up all the broken light
For pity’s sake and put it back where it came from.
Have fun writing light and dark into your novel!