I want the light cast light, but not be visible. where is the visible check box in Rhino 6 ?
Rectangular lights are not visible apart from the light they emit. Can you share a file where they look like they are visible?
rect light.3dm (2.9 MB)
What you see here is the light through glass. It would also show up in a reflective surface like metal.
In this particular case, since the glass you see it through doesn’t really contribute to the rendering in the scene you can hide the glass pane.
This effect also happens in the very latest Blender Cycles version.

edit: after some quick testing, all of the light types may appear visible through transmissive and reflective materials in upstream Cycles, thus also in Raytraced.
I see thanks very much!
@nathanletwory Figure I’d continue this conversation since I think it might be a pitstop for this question, as well – and it’s surprising I couldn’t find the question elsewhere on the discourse:
How do I keep an Area Light from reflecting on high-gloss surfaces? If I’m using an area light to give a soft light to an entire room from above, and it hits a table that’s chrome or glass, it’s a render-killer to have those surfaces blinding white.
That is currently not possible.
