Sunday, 10 July 2016

Copenhagen, 11:50 pm

Since I wrote about long summer days in Copenhagen, the days have grown ever-so-slightly shorter, but even so, twilight lasts from sunset to sunrise. This photo was taken just before midnight. The streaks of light are from an S-train speeding south through Frederiksberg.

Wednesday, 6 July 2016

Day Length and Decision Theory

I am in currently Copenhagen where, 15 days after the solstice, there is no such thing as night. Daytime gives way to civil twilight, then nautical twilight – and that is the darkest it gets.

Growing up in Calcutta, I experienced relatively little seasonal variation in day-length. As far as I remember, it affected my life in only one respect: I was allowed to play in the streets in the afternoon on condition that I'd be back before dark, which meant I could stay out a little later in summer.

The longest day of the year in Calcutta is less than 3 hours longer than the shortest day. In London, where I now live, the difference is almost 9 hours. I sometimes wonder: if I had to choose between Calcutta and London based on day-length alone, which would I pick?

Graph made using data from

Other things being equal, I prefer longer days. By moving to London, I gained about 350 daylight hours in summer, but gave up the same amount in winter.1 The question is, does the loss offset the gain?

Most people are thought to be loss averse: the pain we experience if we lose £100 is more than the pleasure of winning £100, and in general, bad things have more impact than good things. The psychologist Paul Rozin illustrated this beautifully: "a single cockroach will completely wreck the appeal of a bowl of cherries, but a cherry will do nothing at all for a bowl of cockroaches."2

But when it comes to day length, I am not quite sure what I prefer. Sometimes I lean towards more variation, sometimes towards less. Perhaps this means I am indifferent!

A question for the reader: How much variation seems optimal to you? No variation (12-hour days all year, like at the equator), extreme variation (6 months of darkness and 6 months of light, like at the poles), or somewhere in between?

1.In reality the gain is not exactly equal to the loss, but let's pretend it is, for the sake of simplicity.
2.As quoted in Thinking, Fast and Slow by Daniel Kahneman.