Personification is the rhetorical device used to describe light and breezes.
Personification is describing something nonhuman the way you’d describe a human by giving it human actions or qualities.
An example of personification of light is found in chapter 1, when Ralph goes swimming.
He turned over, holding his nose, and a golden light danced and shattered just over his face. (ch 1)
The light is described as having danced. It is also described as having shattered. Neither of these descriptions can really describe light. Both are used figuratively to associate Ralph with light.
Figurative language is also used again to describe light and breezes.
When these breezes reached the platform the palm fronds would whisper, so that spots of blurred sunlight slid over their bodies or moved like bright, winged things in the shade. (ch 1)
The fronds are described as whispering, which is also personification. The “sunlight slid” also is an example of personification. However, it “moved like bright, winged things” as well, which is a simile (a comparison using like or as, rather than a direct comparison). The simile is a similar technique to personification. Sunlight is also described as “crawling” and “fierce.”
The use of personification and other figurative language to describe light demonstrates the importance of light as a motif in the story. Because the light is described as almost human, we see the boys as human. The dark is also personified, especially in the metaphorical beast, as the other half of the same coin.