הדלקה עושה מצוה

There is a principle related to the Chanukah candles, titled: הדלקה עושה מצוה, that the lighting of the Menorah, is what makes the Mitzva fulfilled.

This means that as long as the candles could burn for thirty minutes at the time of lighting, you have fulfilled the Mitzva. If, for example, an unexpected gust of wind came and blew out the candles, even after a few minutes, the candles do not need to be lit again.

This also explains why a blind person is obligated to light the Menorah, even though he can’t see the candles. This is different than the case of the Bracha on smell. If one has no sense of smell, he cannot make the Bracha of בורא מיני בשמים.

But since we say הדלקה עושה מצוה, that it is the lighting that constitutes the Mitzva, the blind man must light the candles even if he cannot see them.