Sri Lanka Standard Time (SLST) is the time zone for Sri Lanka. It is 5 hours and 30 minutes ahead of GMT/UTC (UTC+05:30).[1]
The Sri Lanka Time reverted on 15 April 2006 to match Indian Standard Time calculated from the Allahabad Observatory in India 82.5 ° longitude East of Greenwich, the reference point for GMT.
The entire country shares the same time. Since 1880, Ceylon or Sri Lanka Time has varied between UTC+05:30 to UTC+06:30.
In 1880, it was UTC+05:30. During World War II, in January 1942, when the Japanese were on the verge of invading Ceylon, the time was shifted to UTC+06:00. In September 1942, it was further advanced to UTC+06:30.
When the War ended in 1945, Ceylon reverted back to UTC+05:30 to be the same as India.
In May 1996, it was changed to GMT+06:30 hrs for daylight saving during a severe power shortage in Sri Lanka. The clocks were put back by half an hour to UTC+06:00 in October 1996.
Currently Sri Lanka does not observe daylight saving time, though it was used during the World War II.