O.K. I modified the code. Now, you can click "setup" check box.
Then use mouse to drag the red arrow to change the direction for the light path.
If you want to setup more than one light path, drag the "id" slider and drag the arrow again to setup it's direction. You can click the link "Usage" below the simulation for an flash animation which will show you how to do it. I hope this is what you want.

VIEW or DOWNLOAD ejs xml source
then click to translate strings for selected locale.

Press the Alt key and the left mouse button to drag the applet off the browser and onto the desktop.