Iceland is one of the best places in the world to see the northern lights. A northern latitude combines with a scarcely populated landscape, making for the perfect conditions to see the aurora borealis.
The Langjökull glacier is as good a place as any to see the northern lights in Iceland, but it’s unlikely that you’ll be up on the glacier while it’s dark. You can see the natural light show from the nearby village of Húsafell though.