Daylight Saving Time (DST) exists mainly to make better use of available daylight by shifting clocks so that evenings have more daylight. The core idea has several practical motivations, with energy considerations and social convenience as the traditional drivers. Key points:

• Historical origins: The concept emerged during times of energy scarcity, notably around World War I, as a way to reduce fuel and lighting use by making better use of evening daylight. This origin often gets associated with Benjamin Franklin’s early musings, but formal adoption came later in various countries (typically in the early 20th century).

• Practical rationale: By moving an hour of daylight from the morning to the evening, people can use daylight for activities after work or school, potentially reducing artificial lighting and enabling longer outdoor activities in the evening.

• Energy debate: While DST has been advocated as a means to save energy, modern research shows the impact is mixed and highly context-dependent, varying with climate, behavior, and energy usage patterns. Some analyses suggest modest or even negative net energy effects in certain regions.

• Global variation: Not all countries observe DST, and within those that do, the start and end dates can differ. Proximity to the equator reduces the seasonal variation in daylight, making DST less useful in those regions.

Bottom line: DST is primarily about aligning human activities with daylight to gain more usable daylight in the evenings, with energy considerations historically driving its adoption, though its effectiveness for energy savings is now widely debated.