I to use spotlights for volume light. A couple of tips, use the Light Lab Volume light ( not the Sky Lab )

The light needs to Cast Shadows,  Set the light render options to Visible Object, Volume and Infinitive.

I use Ranged Falloff. This gives me control over how far the light is cast. When volume light over laps other lights in the scene weird things can happen. I also use gradients to set color and help control how far the light range is. (  but this can be very tricky ) Like AS said you will need some front light to make the viewed ( front ) of the objects visible. Range falloff will help keep the normal front lights from overlapping the back volume light.

Use a smoke object ( lick a giant sphere for the hazy smoke in the scene.

 

Volume light renders are very time consuming, so set the scene up with the back spot light using normal light.

Then afterwards set the light to volume and do plop renders to check the volume light in different areas.

 

Here's a scene I did awhile back which is close to what you are after.

Stephen Ray