Translation notes:
Wang Wei was an Amida Buddhist. The home of the Amida was considered to be in the west, so the afternoon sunlight can be viewed as a metaphor for the Buddha's teachings, and the glowing lichen a metaphor for enlightenment.
The title also has Buddhist echos, since the Buddha's first discourse was given in another deer park (a kind of wildlife preserve) at Sarnath.
This poem has been translated many times. There's even an entire book consisting of nothing but such translations, titled 19 Ways Of Looking At Wang Wei.