For the life of me, I can't figure this out, and it should be simple.
I have a photo with a light. I want to mask out the light in the photo and have an AE created light look like it's shining though.
I assumed I'd just draw a mask on the photo, subtract it, make the layer 3D, add a light and wah-la. Wrong. The 3D light simply illuminates the scene. No matter where I position it, it doesn't look like it's shining 'through' the hole of the image.
After Effects doesn't include volumetric lighting that you're after which is a shame. However, there is a third party solution. Trapcode Lux is designed specifically for this and will give you what you need;