Understanding Daylight Savings Time

The Daylight Savings Time is a one-hour shift that is seasonally inserted in some (but not all) Time Zones. Daylight Savings Time is in effect during the summer months, and is usually one hour ahead of Standard Time. In those portions of the United States that observe Daylight Savings Time, it is in effect from the first Sunday in April to the last Sunday of October. Daylight savings time begins when clocks are set from 2:00 a.m. to 3:00 a.m. on the first Sunday in April and ends when clocks are set from 3:00 a.m. to 2:00 a.m. on last Sunday in October (October 26, 1997).

In the United States, the only states which do not use Daylight Savings Time (besides Alaska, which has special ways of dealing with daylight hours due to its very high northern latitude) are Hawaii, Arizona, and most of Indiana. While most of Indiana remains on Eastern Standard Time year-round, some portions near borders maintain the same time as the neighboring state, and therefore do shift to Daylight Savings Time. In particular, five northwestern Indiana counties (Lake, Porter, La Port, Jasper, and Newton), and five southwestern Indiana counties (Gibson, Posey, Vanderburgh, Warrick, and Spencer) are part of the Central Time Zone and shift to Central Daylight Time. Meanwhile, five southeast counties (Harrison, Floyd, Clark, Dearborn, and Ohio) switch to Eastern Daylight Time on their own to stay on the same time as Cincinnati and Louisville. In Arizona, many Indian reservations do switch to Daylight Savings Time, while the rest of the state does not. Since U. S. Eastern Standard Time (EST) is UT-5 hours, U. S. Eastern Daylight Time (EDT) is UT-4 hours.

Time Zone	Hours to add to UT
Eastern Daylight Time (EDT)	-4
Central Daylight Time (CDT)	-5
Mountain Daylight Time (MDT)	-6
Pacific Daylight Time (PDT)	-7

Europe also observes Daylight Savings Time, but the dates on which it goes into effect and ends are different than in the U. S. In the southern hemisphere, insertion and removal are inverted in relation to the northern hemisphere. During World War II, the U. S. and some other countries implemented “double” daylight savings time consisting of a two hour shift.