I read about that and tried it last summer, nothing happened. Though I also read that if it weren't ridiculously dark and very dry it wouldn't work. Thoguh I don't see how external humidity would matter at all, since the second you put it in your mouth it gets really damn humid.
As my poor mother will tell you, if you use a pair of plyers instead of biting the LS it is much easier to see. The down side: Our bathroom had Wintergreen LS pieces in every corner and crevice. Obviously this approach quickly lends itself to making as big a spark as possible using many lifesavers at once.