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.
- 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.