Not exactly. This is done. I want not to blend both the source and destination colors, but add them when writing to the color buffer. This add would never "fade" the colors when blending, then my sparkle would look like light, not a blurred point.
Hmm... Wouldn't that mean to make the lightening "lines" opaque?
Well, I guess, you have to use RenderingAttributes and/or TextureAttributes. But I have never "really" used them. So I cannot provide you more tips than the JavaDocs will give you. Good luck

.
Marvin