DST is in effect in summers, that’s why it is also called summertime. When DST is in effect, we are getting more light in the evenings and less in the mornings. The original reason for shifting time was to reduce power consumption by lighting artificial lights during working hours.
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Today, DST is widely criticized for its alleged effect on human health. Effectively, DST causes jet lag-like effect twice a year by shifting the clock one hour.
Different countries and regions implement DST in vastly different ways, which makes calculating time zone differences confusing and complicated. It is technically not possible to calculate time zone differences in a right way without knowing exactly if and when a particular territory switches to summertime and back. To make things even more confusing, some territories observe DST while others do not. This can happen within different territories within a single country. For example, in the USA states of Hawaii and Arizona do not observe DST.
It is important to know about "time change" but the answer for the question "when is daylight savings" is different for different countries. This site instantly gives you the information when it starts or when it ends for any country of the world. Also site provides you with the information of directions of changes (backward or forward) and value of the timeshift (not all of countries use timeshift for an 1 hour).