Recently, I have been working on a project where a spaceship zooms to a CG earth, and then in the next scene, you can see it slowly landing onto the ground. I am using real footage for the second scene, and I already have it camera tracked. The only problem is that the hover engines of the CG ship are emitting blue lights, and I want the light shining from them to show on the ground of the real motion tracked video. In case if I'm not being clear enough imagine I modeled a flashlight that actually emitted light, and I wanted to CGI it into a video where I am shining an imaginary flashlight onto the ground. With a little bit of masking and object tracking, I would be able to put the flashlight into my hand, but how would I have the light shining from the CG flashlight look like it is shining onto the ground of the video?