date_default_timezone_set('Europe/London');


$datetime = new DateTime('2008-08-03 12:35:23');
echo $datetime->getTimezone()->getName() . "\n";


$datetime = new DateTime('2008-08-03 12:35:23');
$la_time = new DateTimeZone('America/Los_Angeles');
$datetime->setTimezone($la_time);
echo $datetime->getTimezone()->getName();