I remember reading in one of the threads below that the problem of edges of alpha planes showing in volumetric light had been fixed in Vue 5. But here it is again. This render was done at high quality settings, but with "optimize volumetric lights" switched on. Before I try this out in another 8 hour render: - does anyone know if deselecting this option will solve the problem? Thanks!

it seems like the transperancy mask and the leaf pictures do not match. you make sure the alpha matches the image you are applying the mask

Shred, that is not the problem. The mask was generated from the image - what you can see are the outlines of the alpha square. This was a common problem in Vue 4 volumetric renders.

Maybe I should add that other parts of the tree look OK; it seems to have to do with the angle between the alpha plane and the lightsource.

Actually, this is a different problem. What was fixed from Vue 4 was an issue that made the transparent part of an alpha plane appear BRIGHT WHITE in volumetric lights. The problem you are reporting has been around for a while now and has obviously not been fixed.