The quotation "a place where there is no darkness" occurs twice in George Orwell's "1984." That is certainly no accident, given Orwell's writing style and his portrayal of life in a totalitarian society.
In a totalitarian society, especially as portrayed by Orwell, there is no freedom save of one's personal thoughts -- and those are communicated to others at risk of imprisonment or death. Dreams, therefore, represent an escape from the constant repressiveness of the society in which Winston Smith lives. Only through his dreams can Winston reflect on the past and entertain thoughts of the future. When, in a dream, Winston's future torturer O'Brien states that "we shall meet in a place where is no darkness," it can mean multiple things. First is the sanctity of the dream-state, into which the government cannot peek. Darkness in the context of Orwell's use of this phrase refers both to the emergence of a free society where repression, indoctrination, and omniscient surveillance are no longer the defining characteristics of society, and to the lighted prison cell into which no darkness is permitted, lest the prisoner be allowed to sleep. Constant light is a form of psychological torture routinely used even today, as it is an essential component of the use of sleep deprivation as a means of "breaking" a prisoner. In other words, "where there is no darkness" denotes both freedom and repression, depending upon the context.
The dual-meaning of the phrase "where there is no darkness" is consistent with the underlying theme of "1984" and the use of "doublespeak." The notion of "thought police," a central component of Orwell's story, speaks to the importance of dream sequences throughout the book, and that, combined with "doublespeak," provide the context from which Winston's dream about a conversation with O'Brien -- a conversation the content of which would get him imprisoned -- is born.
[as a side note/recommendation, the 2006 German film "The Lives of Others" captures the essence of the totalitarian society and the emergening conscience of a "Winston" quite well.]