Satya Meka has a new quick tip After Effects tutorial at AE Tuts, Add Lux To Your Lights (Without Lux):
Here is another QuickTip for those of you who still haven't procured the amazing Trapcode Suite. Though we advise you get the plug-in yourself, here is a handy little tip to to help generate the look of Trapcode Lux.
Both of the fancy AE Lens Flare filters, Optical Flare and Light Factory, have similar control built-in now. Satya also wrote up some background: Pseudo-Volumetric Point Lights; Magic Behind Trapcode Lux.
In addition see a 2007 AEP post, Volumetric lighting with expressions, on a tutorial and the finished script from Peter Torpey on how to create volumetric lighting using expressions (it even responds to camera movement). Chris Meyer had some related general After Effects advice in 'Light Transmission' and 'Natural Light Effects'.