I'm making an old dusty attic render and I've come across a bit of a problem. (Or several) I'm using 300 samples and the Denoiser, and as you can see in the following picture the rays are not showing very well in the render but they are in the preview, this I could live with, but would still like help and tips on why it is doing that.. What is more, I have a sun lamp on the right side of the model and the rays are coming out on the left side where there is less if any light. My sun lamp is a 5 in emission value and the size is 1, and the light bounces are 1024. What is going on!?
In order to have volumetrics work with a sun lamp you need to create a box around the scene and have it use volume scatter.
Volumetric lighting will not work with a sun lamp and volume scatter used in the world settings (read: Volume Scatter in World makes the sky turn black).
If you are using a window, then the default glass material will not allow for direct light to go thorough. You need to modify the glass material with a node setup like this: