The word light in this quote is part of one of the essay’s motifs. When the author enters the dark house to capture the unknown bird, he uses a spotlight to blind the birds so that it cannot see to escape through the hole in the roof. When his plan is foiled and the bird knocks the spotlight over, giving the bird’s mate the opportunity to escape, the light ends up working against the narrator. The author then locks the bird up in a small box and makes his camp in the darkness.
The following morning, the author holds the bird and notices that he is looking up into the deep, blue sky. The author describes the sky as “so full of light that I could not follow his gaze” (p. 191). The author then releases the bird, against his employer’s wishes, and observes that the bird vanishes “like a flicker of light” (p. 191). Finally, we have the context quote, about how the bird has disappeared into the “towering emptiness of light and crystal that [the author’s] eyes could scarcely bear to penetrate...The light was too intense” (p. 191). The bird’s mate then emerges “[s]traight out of the sun’s eye” (p. 191).
We can see from this greater context that “light” refers literally to very bright sunlight. However, the motif of light is tied to what the author observes about nature and animals: there is something passionate and inexplicable in living animals that machines will never be able to recreate. So in this quote, the blinding “light” symbolizes the unknowable animal nature that cannot be quantified or replaced by machines.