I've heard this koan before but it may not be as straightforward as it seems. On first glance I thought that the lantern would be enlightenment - but the blind guy who says "darkness or light, all the same to me" sounds more like the Zen teacher.
Besides, enlightenment or dharma wouldn't burn out like a candle. So if the blind guy is already enlightened, then the lantern is a useless thing after all. It was certainly of no use to the blind guy or the dude who walked into him.
The lantern. I'm stuck now on what it represents. Maybe I have this completely wrong. It doesn't really matter. It's the thought that counts.