The first line, `czm_getDefaultMaterial(materialInput)`, takes care of defaults so you don't need to set `diffuse`.  Can you show some examples that look like [glow](http://http.developer.nvidia.com/GPUGems/gpugems_ch21.html)?  The current Sandcastle examples don't show it off in the way I would expect.  Here's another [example](http://philogb.github.io/blog/2011/10/14/philogl-1.4.0/).  Both are done with a post-process bloom, which is exactly what I plan for the post-process branch, but it comes at a performance and memory hit - an extra geometry pass, an extra g-buffer, and the post-process pass, so I am game (that's an understatement) if we can do something nice without it for special cases like lines.  The other thing I was wondering is if you experimented with `smoothstep` or other non-linear fade-out curves?