An argument (machloket) from the Talmud:

Beit Shammai says: On the first day one kindles eight lights and, from there on, gradually decreases the number of lights until, on the last day of Hanukkah, they kindle one light.

And Beit Hillel says: On the first day one kindles one light, and from there on, gradually increases the number of lights until, on the last day, they kindle eight lights.

The reason for Beit Hillel’s opinion is that the number of lights is based on the principle:

One elevates to a higher level in matters of sanctity and one does not downgrade. Therefore, if the objective is to have the number of lights correspond to the number of days, there is no alternative to increasing their number with the passing of each day.

Increase your light every day of Chanukah and all year long!