Time Zone
timezone
A region of the globe that observes a uniform standard time for legal, commercial, and social purposes.
Daylight Saving Time
dst
Overview
Daylight Saving Time (DST) is the practice of setting clocks forward by one hour during spring and summer months, then reverting them in autumn. The goal is to make better use of natural daylight during waking hours. Approximately 70 countries observe some form of DST, though the specific dates of transition vary by region.
History and Controversy
First widely adopted during World War I to conserve energy, DST remains controversial. Studies on its actual energy savings are inconclusive, and the biannual clock change has been linked to increased traffic accidents, heart attacks, and workplace injuries in the days following the transition. Several countries and U.S. states have moved to abolish the practice.
Impact on Software
DST creates significant challenges for software systems. During the "spring forward" transition, one hour of local time simply does not exist. During "fall back," one hour occurs twice. Developers must rely on the IANA time zone database and avoid storing local times without offset information to handle these edge cases correctly.
Was this article helpful?
Related Terms
Related Articles
Daylight Saving Time - How Clock Changes Affect Global Coordination
Understand how daylight saving time works, which countries observe it, when transitions occur, and how DST complicates international scheduling.
Daylight Saving Abolition - Why More Countries Are Ending the Clock Change
Daylight saving time has been losing political support for a decade. The European Union voted to abolish the clock change in 2019, and medical evidence about heart attacks and circadian disruption keeps mounting. This article surveys the science, the energy myth, and what each region has actually decided.
How Time Zones Work - Understanding UTC Offsets and the Global Time System
Learn how time zones divide the world into regions with different local times, how UTC offsets work, and why some zones use half-hour increments.