Lighting candles of Mikdash:[1]

All seven candles of the Menorah were lit at night. By day, only the 6^th [and 7th] candle, was lit.[2] This candle was called the Ner Hamaravi. The reason for this is as follows: Night represents a time of spiritual darkness, a time for evil forces to come out and wander. At this time, it is most necessary to have spiritual light come out and shine the darkness, hence banishing the evil. During the day however there is not much need for spiritual light, and hence only one candle was lit. On a deeper scale, this is explained as follows: The seven candles of the Menorah represent the seven Midos of Kedusha, from Chesed until Malchus. Now, these seven Midos also exist in Kelipa, such as the Mida of love of G-d in Kelipa exists as a Mida for physical lusts, and a fear of G-d in Kleipa exists as a fear of foreign items as well as anger. Through lighting the seven candles at night one transforms these Midos of Kelipah to Kedusha. Light comes from Chochma, and it is the light/Chochma of the candles that refines the evil Midos.

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[1] Torah Or Vayeishev p. 29a

[2] This follows the opinion of Rashi Menachos 86b; Tosafus ibid; Ramban; Ravad; Rashba; Implication of dialect of Avoda of Yossi Ben Yossi Kohen Gadol, printed in Seder Avoda of Yom Kippur in Siddur Arizal and Admur [letter in Likkutei Sichos 23/354]