SQL & PL/SQL

Hi,
I have a simple select and in the WHERE clause if I use LIKE with a date field it does not work but it works with a string field. For example:

--does not work. does not bring any rows
Select * From MyTab
Where  time_period Like '%';

--works and brings ALL data
Select * From MyTab
Where  level_code Like '%';

Where time_period is of DATE datatype and level_code is VARCHAR2.