Get timezone name in codeigniter

I use the date helper in CI to save the timezone of the user when he signup eg: UM45.

I want to set the timezone of each user based on that and display the date time correspondingly, using date_default_timezone_set().

But that accepts only string.. How can I get the name of t开发者_开发百科he timezone based on UM45?

Seems it can be done via the Language Class:

$this->lang->load('date_lang');
$this->lang->line('UM45');