President's foreword
Thank you for visiting the ACHED association’s website.
The clock change scheduled for March 29, 2026 is now very close. The media and public authorities will no doubt remind everyone to exercise caution in their movements and activities; they will be right to do so. Our association points to an increased risk linked to sleep deprivation and loss of temporal reference points caused by the clock change, both in the direction of advancement and delay. However, this immediate vigilance should not preclude a broader examination. In the current context of oil and climate crises, it is essential to relate the issue of legal time to energy, health, and environmental challenges, to seriously assess the impacts of advanced legal time and to contribute to the search for urgent solutions.
We hope you will find useful information here, capable of informing your thinking and, if you wish, encouraging you to take action.
Since last December, we have undertaken a thorough overhaul of the website. The objective is to make available the association’s documents, the existing scientific references, analytical materials, as well as links to current developments. This effort is accompanied by a restructuring of the site, whose previous architecture dated back to 2004. We have adapted it to current standards, opened possibilities for interaction, while ensuring data security.
Substantively, we seek to avoid terminology that introduces confusion or emotional bias, in order to remain as close as possible to physical realities and observable effects.
The terms “summer time” and “winter time,” for example, are overly simplistic.
“Summer time” may refer either to a time shifted by one hour relative to geographical time (+1), or to a double shift (+2).
In France, “winter time” corresponds to +1 and “summer time” to +2.
These labels, which place French summer time (advanced by two hours) on the same level as Italian or German time (advanced by only one hour), are misleading and lead to unfounded reasoning. In reality, German summer time corresponds to French winter time.
It is therefore important to clarify that France’s current legal time does not strictly correspond to its natural geographical time zone. This situation results from historical decisions, particularly those linked to the Second World War, whose effects persist today. France, which was at UTC+2 at the end of the Occupation, only moved back by one hour in 1945 instead of two, thereby maintaining a one-hour advance over its geographical time zone.
In 1975, in the wake of the oil crisis, the French government introduced an additional hour of advance in summer starting in 1976, placing metropolitan France two hours ahead in summer. This event led to the creation of our association a few years later and remains the reason for this website today, since a measure that was intended to be temporary has never been reversed.
The website is now available in several languages, in order to facilitate information and coordination at the European level, particularly with France’s neighboring countries.
With regard to clock changes, a consensus appears to have gradually emerged against the principle over several decades. However, perceptions remain mixed. Many people appreciate the return in autumn to a time closer to solar time, as well as the additional hour of sleep it provides. Others associate the March shift with longer days and the arrival of warmer weather. These perceptions, while understandable, do not address the underlying issue.
From a scientific and health perspective, the association was founded by a pediatrician with the aim of protecting children and their parents. From its inception, the association has explicitly opposed summer time, rather than the sole principle of changing the clocks. Over the years, numerous studies have highlighted the health effects of advancing the clock. In 2019, empirical studies made it possible to quantify them, showing chronic sleep loss as well as associations with several diseases.
From an energy perspective, available analyses often present significant limitations. They frequently focus on lighting, leaving aside essential components such as heating, air conditioning, or transportation. Some institutions have thus produced partial analyses without covering the full range of energy uses.
Historical data show that changes in energy consumption cannot be attributed to a beneficial effect of time advancement. They are primarily explained by structural factors and transformations of the energy system.
Beyond energy, overall consumption has also evolved. A simple line of reasoning nevertheless allows us to outline a logical chain: time advancement, sleep loss, increased waking time available for consumption, deterioration of health, and increased consumption.
At the institutional level, the situation remains uncertain today. A vote of the European Parliament in 2019 endorsed the principle of ending clock changes, without resolving the question of which time should be retained. Since then, decisions have been postponed.
More recently, statements have reaffirmed a consensus in favor of ending clock changes, while announcing further studies. This situation maintains a prolonged state of waiting.
At the same time, the international context has evolved, particularly in terms of energy. According to ACHED, these developments do not justify maintaining the status quo, but should instead lead to a reassessment of current choices.
We thank you for your attention and for your interest in these issues.
