The Zohar, Chapter “Ve’Eleh Toldot Itzhak (These Are the Generations of Isaac),” Item 165: Because the domination of the Sitra Achra is only at night, Esau’s ruling is only in the exile, which is night, meaning when it is as dark as night for us. This is why the angel fought with Jacob and struggled with him at night, and when the morning came, the strength of the angel waned and he could not overcome him. And then Jacob prevailed because Jacob’s dominion is in the day.
We think that the presence of the Light of Hochma during the day brings us daylight. But that is not the case. Rather, the Light of Hassadim is present during the day; therefore, the Light of Hochma becomes revealed. At night, the Light of Hochma shines without being clothed into the Light of Hassadim; while during the day, it is clothed in the Light of Hassadim. Day is the addition of Hassadim, and that’s why there is light. There is no Hassadim at night, hence there is darkness. The Light of Hassadim reveals (manifests) the presence of the Light of Hochma around us.