Standards: Daylight Saving Time (DST)

Daylight Saving Time (DST) is a widely used system that adjusts the official local time forward from the official standard time during summer months, usually by one hour.

The Energy Policy Act of 2005 changed the start and end dates of Daylight Saving Time in the United States. As of 2007, DST begins on the second Sunday in March and ends on the first Sunday in November. The U.S. Department of Energy (DOE) is required to study the impact of this DST extension, and the U.S. Congress has retained the right to revert back to the previous DST schedule if it cannot be shown that there are significant energy savings.

In the United States, the law that governs the use of Daylight Saving Time is the Uniform Time Act of 1966. This Act provided a standard for establishing the dates when DST begins and ends in the U.S., while allowing local exemptions from its observance. States that wanted to be exempt from DST could pass a law exempting the entire state. The states of Arizona and Hawaii do not observe DST. However, the Navajo Indian Reservation in Arizona does. In addition, American Samoa , Guam , the Northern Mariana Islands , Puerto Rico , and the U.S. Virgin Islands do not observe DST.

Approximately 70 countries observe DST .

Additional Resources:

• Daylight Saving Time Rules
• Time Exhibits
• The Seasons: Spring, Summer, Fall and Winter
• Standards: Leap Year
• National Institute of Standards and Technology (NIST)