[I was asked to post this question by a user who doesn't have access to MY]
According to the OU website
The Beis Ha Levi rules that once the flame is dark and is going out, it is already as if it is totally doused and there is no more mitzvah even though there is still a flame there; the reason being that such a flame has no beauty and is not at all recognizable as being for the mitzvah. (What this is most probably referring to is when there is only a blue light coming out of the candle, without any yellow or orange).
Does this mean that, at least according to the Beis HaLevi, if the Chanukah candles must last for 30 minutes, but during the last minute of the 30 minutes the flame is weak like he describes, is the person not yotzei the mitzvah? Do any later authorities rule like this Beis HaLevi?