Qt LGPL with Closed Source Software

Using Qt enables the software to be closed source when you "redistribute" it. (It is an important concept. E.g., Google uses GPL Linux kernel "internally" to avoid licensing issue")

So, with Qt's LGPL:

• Dynamically link the Qt library, with your source code closed.
• The installer can download the Qt library if needed.
  
• If you modify the Qt library, you must open up the change.
  

Note:

• You might need to provide your object file. (so people can re-link with the Qt's library)
  
• Ask a lawyer if you are in a serious business, or the licensing violation can be very expensive.