They are fullbright yes but they don't have to be if you mask them making them gray. ~ with translucent texture layers.. and if needed, don't let the surrounding sector touch them..
I agree that it would be a little more work.. you should actually be able to achieve the same effect a different/easier way by using dyno lights in a colored sector (if they were introduced to the render as a square texture/layer instead of a sphere.) but we make due with what we can, while we can.
I know, as is, it should be possible but they also kill frame rate at some point.
So I suppose those are the options:
gradient colored 3d floors
add a bunch of dyno lights/less fps impact the better.
or all of the above
It's totally possible to pull off the effect, but there's different ways it could be done.
Real issues is, it would be nice to just select the data type and increase its intensity and be done with it (inside a 3dfloors control sector).
So I guess, why not just set a flat to glow and put a 1 unit brightmap flat above its floor, then 3dfloors (same method) above each, gradually being more translucent?
~ I'm trying to remember when using this method if the thin 1 unit floors had to be 1 unit apart from each other (dead space) or if they are ok now days as is, butted up against one another.
But in the end you might have a half dozen stacked 3dfloors in a given area in the level.
Anyway, there's a few things to take in mind I guess.