The Clock Change: A Story of Time, Light and Clocks
Today we take for granted that the clocks change on the last Sunday of March and the last Sunday of October. This practice, which has become a common norm throughout the European Union, has not always been consensual or straightforward. The clock change has deep historical roots and is closely linked to the evolution of timekeeping, to horology and to the social and economic rhythms of recent generations.
Before the invention of mechanical clocks, time was measured in a far more organic way. The Sun was the main regulator of daily life. Days began at sunrise, and the hours were calculated according to the available sunlight. In Babylon, for example, twelve hours were counted between sunrise and sunset, which meant that the length of each hour varied throughout the year. Later, solar noon — the moment when the Sun reaches its highest point in the sky — was adopted as the reference. From that point, the day was divided into two halves: twelve hours before, twelve after. Even so, these “hours” remained flexible, shifting with the seasons.
With the Industrial Revolution and, above all, the advent of rail transport, it became imperative to establish an exact, uniform time synchronised between towns. Organising train timetables and other logistical activities required precise coordination, which led to the standardisation of national time zones. All clocks now had to agree with one another. Many parishes synchronised with the official time brought from the capital.
The idea of changing the time to make better use of daylight emerged long before it was put into practice.
In 1784, Benjamin Franklin, then living in Paris, published an essay on saving daylight in which he suggested shifting the hours of human activity according to the seasons, to avoid wasting candles. In Spain, the city of Cádiz introduced a similar measure as early as 1810, changing the hours of public services between May and September. In 1895, the New Zealander George Hudson proposed an official two-hour shift.
However, it was only during the First World War that the clock change was actually adopted, for practical reasons.
It was Germany and the Austro-Hungarian Empire that first officially introduced the clock change, on 30 April 1916, in an effort to reduce energy consumption.
Portugal followed suit shortly afterwards, with the first clock change decreed on 17 June 1916, during the government of António José de Almeida (then Minister of the Interior).
The rule established that the change should take place from 1 March, and so it was done between 1917 and 1921. After several interruptions in the following years, it was only in 1926, under the government of António Maria da Silva, that the practice was resumed more systematically, albeit with periods of suspension, as in 1930 and 1933.
Under the Estado Novo, especially during the years of the Second World War, the clock change became more regular, and in 1949 an easy-to-remember formula began to be applied: summer time started on the first Sunday of April at 2:00 a.m. and ended on the first Sunday of October at 3:00. This system remained in force until 1966. From then on, and until 1976, the clocks were no longer changed.
After 25 April 1974, which marked the end of the dictatorship and the return of democracy in Portugal, many administrative and political measures were reviewed — and one of them was precisely the reinstatement of the clock change. The practice had been suspended for some years, and was only reintroduced in 1976, in the midst of the country's reorganisation. The context was similar to that of other periods: energy saving and harmonisation with the other European countries, which had by then already reinstated summer time.
For twenty years, Portugal adopted its own rules for summer and winter time, usually starting on the first Sunday of April and ending at the end of September. In 1992, the government of Aníbal Cavaco Silva decided to align Portuguese time with Central European time, temporarily abolishing winter time. The experiment lasted four years and had controversial consequences, such as an increase in road accidents and disruption to the rhythm of daily life. The measure was reversed in 1996 by the government of António Guterres.
Since then, Portugal has followed the European directive that standardised the clock change across all Member States: at 1:00 a.m. on the last Sunday of March, clocks go forward one hour (summer time); at 2:00 on the last Sunday of October, they go back one hour (winter time).
The next clock change will take place in the early hours of 30 March 2025.
Clocks must be put forward one hour: at 1:00, they will show 2:00.
The clock change remains a subject of debate. Supporters point to advantages such as making use of natural light at the end of the day and potential energy savings. Critics, on the other hand, highlight the negative effects on sleep, on well-being and on productivity. The European Parliament went as far as approving the end of the clock change, but the member states have yet to agree on which time zone to adopt permanently.
In horology, this change marks a symbolic moment. Digital and electronic clocks can adjust themselves automatically via a radio signal (such as DCF77), GPS or an internet connection. With mechanical timepieces, however — especially wristwatches and tower clocks — the adjustment is still made by hand.
For many enthusiasts, this gesture is a small ritual, a reunion with time and with tradition.
And so, between light, shadows and gears, the clock change is also a mirror of our relationship with time. It is a habit that has spanned centuries, wars, regimes and technologies, and which continues to mark — literally — our days.
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