The idea of "night" comes from the idea that there is a period of darkness that envelops Eliezer's life from the time he and his family are deported to his liberation at Buchenwald. The "night" is a moment in time where he became invisible to others, and to himself. It is in this instant where values were inverted. The elements that should have defined reality were noticeably absent. The concept of "night" can actually be seen in the poem that is written in the third section. Examine the first line of the poem:
Never shall I forget that night, the first night in camp, that turned my life into one long night seven times sealed.
This idea of Eliezer's experiences being enveloped or sealed in a period of life that he can only refer to as "night" becomes extraordinarily powerful and a reason to title the work as such.