Daylight Saving Time

I hate Daylight Saving Time. It’s a huge pain to administer (I lose track of which clocks change themselves automatically and which need to be reset by hand), it’s handled inconsistently from region to region in the world (making managing international scheduling and communication more difficult), and it disrupts everyone’s sleep patterns.

Despite the diversity of confusing explanations for why so many places use DST, the underlying justification is actually quite simple: DST is based on the theory that the start of the working day should be correlated with the time the sun rises.

When the days are at their shortest in winter, things are arranged in most places so that people wake up near sunrise in order to get to work for normal business hours. In London the latest sunrise is 8:06,[^The latest sunrise actually happens almost two weeks after the shortest day—“solar noon” shifts back and forth over a half-hour range throughout the year.] which is largely compatible with a working day that starts at 9. As the days get longer in summer, however, sunrise gets far earlier; with no DST the sun would rise at 3:43 on the longest day of the year. The theory is that these extra hours of daylight before the 9 o’clock start of the work day are wasted, since people normally just sleep in to maintain their daily routine before work. Daylight hours in the evening, however, have value: the vast majority of people don’t go to bed on any day until after even the latest sunset of the year (which is 21:21 in London even with DST), so every extra hour of daylight at the end of the day is one less hour that artificial light is required. The DST system partially addresses this problem by shifting sunrise forward when the days get longer: there is a natural variation of almost four and a half hours at London’s latitude, but DST brings this down to three and a half.

If you buy this (fairly reasonable) story that people want to wake up at roughly the same time with respect to sunrise, and maintain the same morning routine throughout the year, then DST is a very crude tool: in summer Londoners are still “wasting” two or three hours of daylight before they get up in the morning. An ideal system would start the work day roughly 90 minutes after sunrise every day. Setting your clock to sunrise at 7:30 every morning would mean that on the year’s longest day the sun would not set until eight minutes past “midnight”, which would eliminate almost all need for artificial lighting on that day.

I’m currently working on such a system. Stay tuned…