Light trails

I’ve been wondering how it would be possible to achieve a light trail effect in animations, ideally via post-processing… would like to know this for both Blender Internal and Cycles if possible. The effect I’m referring to is pretty much a form of motion blur, except the “ghosts” stick around based on the brightness of the object producing them: Normal objects don’t cause any blur, while light sources leave a long hard trail lasting a few frames. Here’s an example image that shows the effect in an exaggerated form:

I figure that at worst, I can just have the light source spawn static halo particles each frame… but that’s an ugly workaround and much more limited compared doing this correctly. Is there such a thing as a light sensitive version of the vector blur node?

Doing this effect in post process only wont be possible, or crappy…
One possible way is to use real motion blur in cycles ,with shutter set to more than one frame… That’s a bit overkill but that should work.
Personally I’ll cheat and use curves with bevel and emissive material… You can then add some glow in post process.
you can get inspiration from this tutorial :

That is a helpful tutorial, thanks! I would imagine this being done ideally by having light sensitivity as an option for the Vector Blur node, but using an animated texture can work too in some cases. Your idea with the shutter is also helpful, I’ll keep it in mind!

Blender’s shutter option for motion blur is only effective over smaller durations or shorter movements, as they tend to become inaccurate over longer distances. Otherwise use multiple frames merged using mix nodes.

Gleb actually covers this exact thing in his new Lighting Hacks course. Check out tutorial 7.

Also vector blur in the compositor works quite well, especially on a render layer.