point-density node experiment
For this animation I used the gooseberry-branch of blender 2.75. I made a volumetric material using the point-density texture node to create a cloud and added some red point lamps to a second particle sytem from the same emitter.
you can download the blend file here
If you want to run this blend file make sure you use the gooseberry branch of blender 2.75 - the point-density texture node isn't available in the stable branch yet
See also:
AN experiment - force field curl clusters
twisted torus particles
particle density volumetric material
Volumentric emission shader