Need help with Dust or particle that can show in light and hide in dark place

Hi, I'm create a horror game that use a flashlight. I've already create dust from particle system in the dark room and now i'm trying to figure out how to hide this dust in the dark place and only show when there is a light source (ex. in front of my flashlight).
I only know that I can use volumetric light and dust particle for light bulb or unmoving light sources But I want my flashlight that can swing and look around map to show a dust in the dark room too.
Thank you.

(something like this pic)

 

Okay. I just figured it out with using quad Mesh instead of Billboard in Renderer and it work.

 

Use a transparent lit shader for the particles, then they will be reacting to lighting.