I also used to wonder about that when I first started coming to Sweden. Over the years, I’ve come to understand it’s a surprisingly complex thing. Now that I live here, I do it, too.

It may appear wasteful, but it’s not. The bulbs used for these typical window lights have always been low powered, and in a country that relies as heavily on hydro power as Sweden does, the national conscience has traditionally been quite clear about letting those 95% of the energy an incandescent bulb consumes contribute to the home heating effort, and dedicating the remainder to good causes as I will try to speculate on below.

These days, it’s all LED, of course. I use 1.6W bulbs.

Here’s what I think it’s for:

• it’s a Swedish tradition to contribute to a sort of "pretty city image" by having little lights in the windows; it literally lights up the street, makes the place lived in, and friendly. When I’m in Germany, with its drawn curtains or lowered blinds, the streets at night just seem dead, deserted, and the houses seem to say "keep out". In Sweden, it’s very much the opposite.
• the Swedes are a very communal people; seeing signs of life in the neighbour’s house reassures them that they are not alone, and it is my impression that many leave their lights on "for their neighbours";
• having lights on in the house is a security measure, making the house look occupied. I also feel safer when they are on when I’m not home. Maybe that’s just common sense.
• windows are what the light usually shines in through during the day; during the dark season, it makes sense to have lamps in the windows to maintain those dynamics. I have a little lamp in every window, too, and it seems to create an illusion of daylight if one chooses to see it that way.
• it satisfies the home owner to have a cosily lit home to return to in the dark months.
• it actually makes the house look better, and beauty is a big deal here. Sweden is very much about visual beauty, and lights are an excellent way to achieve it.

Some illustrations of what we are talking about: