Why Do We Have Daylight Saving Time? An Energy Measure That Stopped Saving Energy
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Twice a year most of Europe and North America move their clocks, on the reasoning that shifting the working day relative to daylight saves energy on lighting. The reasoning was sound when it was adopted and the world it assumed has largely gone, which is why the measure is now defended mainly on other grounds and why abolishing it keeps being proposed and keeps not happening.
Where it came from
The idea is usually credited to William Willett, a British builder who campaigned from 1907 for advancing the clocks in summer, and to George Hudson, a New Zealand entomologist who proposed a shift in 1895 to give himself more evening light for collecting insects. Benjamin Franklin is frequently cited and was joking, having written a satirical letter suggesting Parisians be woken by cannon to economise on candles. Neither campaigner succeeded on the argument. What produced adoption was war: Germany and Austria-Hungary introduced it in April 1916 to conserve coal, Britain followed within weeks, and most combatant nations did the same. It was repealed in several countries afterwards, reintroduced during the Second World War, and made permanent in many places after the oil crisis of 1973, which is a consistent pattern in which the measure arrives whenever energy supply becomes a pressing national concern and is questioned whenever it does not.
Whether it saves anything
The original case rested on lighting, which was a large share of household electricity when incandescent bulbs dominated and demand peaked in the evening. Several things have changed that calculation:
- •Lighting is now a small fraction of household electricity use, since efficient bulbs consume a fraction of what incandescent ones did
- •Heating and cooling dominate instead, and shifting the day can increase both, since people are awake during a darker colder morning and an earlier hotter afternoon
- •A natural experiment in Indiana, where counties adopted the practice at different times, found household electricity use rose slightly rather than falling, driven by air conditioning
- •Studies elsewhere have found effects ranging from a small saving to a small increase, with most modern estimates clustering near zero
- •Transport fuel use may rise, since lighter evenings are associated with more discretionary driving
- •The energy argument is therefore no longer the reason the practice is retained, whatever the legislation says
The health and safety evidence
The clock change itself, rather than the summer schedule, produces the clearest measurable effects, and they are almost all associated with the spring transition when an hour of sleep is lost. Studies have reported small increases in heart attacks and strokes in the days following the spring change, an increase in road collisions on the following Monday, more workplace injuries, and effects on mood and on judicial sentencing. The autumn change produces smaller effects in the opposite direction. Separately, sleep researchers argue against permanent summer time specifically, on the grounds that human circadian rhythms are set principally by morning light, and that permanently shifting clocks forward means darker mornings all winter, which would push the population further out of alignment with the sun. That position, held by major sleep and chronobiology societies, favours permanent standard time, which is notable because most political proposals to end the changes propose permanent summer time instead.
Why it persists
Abolition is repeatedly proposed and repeatedly stalls, for reasons that are structural rather than scientific. The European Union voted in 2019 to end mandatory changes, with each member state choosing its permanent offset, and the decision has not been implemented, partly because neighbouring countries choosing differently would fragment the single time zone arrangement that trade and transport depend on. The United States has seen bills for permanent summer time pass the Senate without becoming law, and the country tried permanent summer time in 1974 during the oil crisis and abandoned it within months when dark winter mornings proved unpopular, particularly for children travelling to school. Businesses in retail, leisure and tourism favour light evenings and lobby accordingly, while agriculture has historically opposed the change, contrary to the popular belief that farmers wanted it. Meanwhile most of the world does not observe it at all: it is largely confined to Europe, North America and parts of the southern hemisphere, and almost absent in the tropics where day length barely varies.
The takeaway
Daylight saving was adopted by combatant nations from 1916 to conserve coal for lighting, and lighting is now a small share of electricity use, so modern studies find savings near zero and sometimes a small increase from heating and cooling. The spring transition is associated with measurable rises in heart attacks, road collisions and workplace injuries. Sleep researchers favour permanent standard time because morning light sets circadian rhythms, while most political proposals favour permanent summer time.