TimeZone.IsDaylightSavingTime Method (DateTime)
Returns a value indicating whether the specified date and time is within a daylight saving time period.
Assembly: mscorlib (in mscorlib.dll)
The year to which the daylight saving time period applies is derived from the time parameter.
Because the TimeZone class supports a single daylight saving time adjustment rule, the method applies the current adjustment rule to any date, regardless of whether the adjustment rule was in effect on that date. Assuming that the operating system itself has accurate historic daylight saving time data, a more accurate result is available by using the TimeZoneInfo.IsDaylightSavingTime method. Whenever possible, use the TimeZoneInfo.IsDaylightSavingTime method.