The liberation of Denmark 5th of May 1945 was announced the evening before, at May 4th. During the war, people had been forced by the Germans to darken all windows in the evening, in attempt to make orientation difficult for the allied. The cities were completely dark all night. As soon as the message of liberty had reached Denmark, people threw their black curtains away, and put lit candles in the window instead. Light, light, light, everywhere.
This has been a tradition ever since, to put lit candles in the window at May 4th, to celebrate liberty.
The 5th of May are celebrated all over the country, to honour the fallen soldiers and freedom fighters.