You can drag the light source to different place or change the index of refraction for the material.
If the index of refraction is larger than 1.414 (square root of 2) , all the light enter the fiber will be totally reflected at the boundary.

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.