The sanctity brought to light during the exodus becomes a permanent fixture in the life of the Jewish people with the Shalosh Regalim, each reflecting a particular aspect of Divine revelation. In other words, Klal Yisrael enters a new dimension, a world apart from the humdrum drudgery of the nations. Removed from the dark confines of a limited influence, they bask in the blinding light of a supernal realm, seeing G-d at every turn. This was a level of Kedushah written for eternity, enlightening all the world to G-d's word. Chanukah, on the other hand, is a private affair - Ner Ish U'Beiso.
Darkness is cause of two problems.
Firstly, in the absence of light, man cannot see where to turn, the likelihood being that he will stumble and fall. In addition, at times one may confuse a pillar for a man, right from wrong, or vice-versa. This error is a more serious mistake, for, certain that he had seen a true picture of his surroundings, he proceeds with careless abandon. The Shalosh Regalim illuminate a new horizon, lifting our spirits in protection, lighting up the long, dark night of the physical world. If Purim is the dawn at the edge of night, Chanukah, that follows, is part of the day.