Az-Zulumāt and an-Nūr are interpreted in two senses:
1. Az-Zulumāt is used in the sense of shirk (associating partners with God), and an-Nūr in the sense of iman (faith); as in the following verses:
Allah is the walī (friend and protector) of those who have iman; He brings them out from zulumāt (that is, from shirk) into nūr (that is, into iman). (al-Baqara 2:257)
A similar expression is also found in the same verse.
He and His angels send blessings upon you so that He may bring you out from zulumāt (that is, from shirk) into nūr (that is, into iman). (al-Ahzāb 33:43)
There are many similar verses.
2. Az-Zulumāt is used in the sense of night, and an-Nūr in the sense of day; as in the following verse:
All praise is due to Allah, who created the heavens and the earth and made the zulumāt (that is, the night) and the nūr (that is, the day). (al-Anʿām 6:1)
In the Qur'an, there is no other command like this (that is, the use of zulumāt and nūr in the sense of "night" and "day" is unique to this verse).