I try to (re)use, by copying it on an image of mine, the following image:
http://fr.wikipedia.org/wiki/Fichier:Glasbutton_rot.svg
where, in fact, I suppress the inkscape logo, sorry

The trouble is that the nice transparency and light effect depends on the place where is located the button on the page. More precisely, at the place where I want to put it on my image, this button is completely dark! So, I guess that I should either create another light source or, at least, move the image's one. But I have no idea how to do that.
Thanks in advance for any hint

Regards,