Northern Lights in Greenland can be observed from end of August to beginning of April, but especially deep in the winter. If you are travelling to Greenland during that time you have great chances of seeing these multicoloured lights dancing through an arctic night.
Northern Lights, also known as aurora borealis, can be seen very well in the area of Kangerlussuaq due to its stable micro climate. But of course northern lights in Greenland can also be seen in many other places, like Disko Bay, East Greenland and Nuuk. Remember, the more time you spent in the great outdoors, the higher your chances of seeing them are.