Both Dylan Thomas and Robert Frost were well-"acquainted with the night." Both poets experienced tragedies and the dark side of humanity; Thomas was an alcoholic and a drug abuser, while Frost was a victim of mental illness (he watched family members become institutionalized, and he struggled with depression himself). It is no surprise, then, that both poets delved into the dark side of humanity with their poems "Do Not Go Gentle...." and "Acquainted with the Night."
One of the most popular symbolic representations of "night" is physical death. Of course, this interpretation of "night" makes sense; after all, on a literal level, Thomas' poem "DNGG" was intended for his dying father. Dylan Thomas urges his father to "rage, rage against the dying of the light" because, though his father was an imposing sort of man, Thomas still wants to remember him as someone who fought for life, even until his death. Accordingly, we could use this interpretation of "night" as representing physical death in Frost's poem "Acquainted with the Night." Frost was, in fact, acquainted with death; his father died of tuberculosis, and his son committed suicide. In that sense, Frost had "...walked out in rain...." (his father's death) "...and back again...." (his son's death).
Other meanings of "night" in these poems include references to figurative deaths. Thomas could never show his father "DNGG" because he claimed that "he was the only one who didn't know he was dying," which suggests a longing -- on Thomas' part -- for his father to live out his last days with some zest. Frost's poem, on the other hand, obviously harbors a tone of melancholy recognition throughout -- a recognition that, as he enters the physical night, he also absorbs all the dark emotions that go along with the sights and sounds of darkness.
In both poems, "night" is a symbol of depression. Also in both poems, "night" is one side of a clear light/dark dichotomy. In "DNGG," "night" and "day" are the obvious opposites, representing general evil and goodness, respectively. We see other symbols and images of living life to the fullest and going towards the "light" of life in "DNGG" ("Blind eyes could dance like meteors and be gay," the image of "lightning" as a desirable attribute during life). In "Acquainted....," Frost mentions "light" as something that is far from him ("I have outwalked the furthest city light;" "O luminary clock against the sky"). Both poets feel a sense of loss and hopelessness, surrounded by the darkness of depression, but there's more of a sense of urgency in Thomas' poem. Thomas obviously wants control over these "dark" circumstances; Frost has become more resigned to his circumstances.
Overall, here is a succinct list of possible meanings of "night." Instead of looking for scholarly articles on the meaning of "night" in these poems, in this case, it actually makes more sense to relate the poets' lives to their products:
1. physical death
2. emotional death
3. spiritual death (if you have questions about this, just ask me)
6. mental instability
7. loss of vivacity