Twilight Render User Forum

The faces can only be combined to one face if they are coplanar. Smoothed surfaces are not really one face. You may ask if your object really needs so many faces.

I am thinking the same about a neon tube I am doing. I do need the active glow on the back and the front ,might work as passive/fake (2 surfaces) but does the shape really need to be round with many facets in this particular view to get a good effect?

Please try attached scene.
volumetrics scenes can be finicky, for sure.

Perhaps for the neon tube, you could try this fake neon material by Ecuadorian.
Subject: Emitter materials