They definitely are not illuminating in a tube shape
Tube Light is a bit of a misnomer - it is a light with length. The Radius is only visible in reflections.
Light is emitted across it’s entire length. However, shadows are cast from the origin point - it does not cast shadows in a GI sense.
(It is not an area light, as someone suggested)
Very interesting, I’ll try that today, thank you for the rendering !
I use this and it really works well. 
this post is from **2014 **