The Talmud states that G-d created light and charged it with the commandments of the daytime, and darkness and charged it with the commandments of the nighttime. The Netziv (Meromei Sadeh) observes that the Talmud appears to be stating that darkness is a creation, and not merely the absence of light. This is the position of the Vilna Gaon (in Kol Eliyahu, based on Yeshayahu 45:7, and explaining Shemot 10:21), although many rishonim appeared to understand differently (such as Ramban, Shemot 4:11; Ran , Derashot 3; Rambam, Moreh Nevuchim, I, 73:7; see also R. Yosef Engel, Gilyonei HaShas to Yerushalmi Berachot, #47). The Sefer Chavatzelet HaSharon al HaTorah (Shemot, pp. 102-103) discusses this and notes that even if one maintains that darkness is an active creation, that would only apply to the darkness of night, as indicated by the relevant sources; the darkness created by covering up one’s windows during the daytime, for example, would merely be the absence of light. (See also Resp. L’Horot Natan, V, 55:3).