This should be quite simple, im just having a little trouble.
Imagine shining a torch through a cheese grater in the dark, you would get lots of little light beams, they would move about as you moved the torch etc.
I want a similar effect, but i have a layer with an ornate shape cut from it, using a mask, rather than a cheese grater. I then want to shine a light through from the other side of the said ornate mask and hopefully get some interesting beams of light.
I couldnt get anything to work with the standard lights in AE, (the light beams just didnt show up) so i had a go with a trapcode lux layer, hoping it would help make the beams appear, which they did, but my ornate cheese grater layer then disappeared!
You might also look up "disco ball" in various AE tutorial sites. it uses only the stock filters but it will not create true, 3D, volumetric light beams. Fro that you must have a more sophisticated filter like Trapcode.