I found the following explanation (Don't know if it is available for 10.5). Note that the DB2 engine is
the same, just doesn't have some add-on tools including in the download.:
The DB2 Express-C database server is downloaded worldwide, but broadband internet is not yet
universal. Because of this, we are releasing a light version of DB2 Express-C 9.7.2 for Windows. It's an
amazing 44% smaller than the full download.
Unlike the lighter download, the DB2 Express-C (full) includes the Control Center, Full Text Search,
Configuration Assistant, and the First Steps wizard. It also has support for non-English languages in its
user interface. However, if you don't need these features, you can grab the DB2 Express-C (light) for a
quicker download and a simpler installation.
For example, if you are setting up a DB2 database on a Windows server that you plan to administer
remotely with Data Studio, then the light version of DB2 Express-C is a great choice.