Assuming in my scene there are no lights, no hdri maps, just a simple plane and a sphere, I'm expecting to hit render and see nothing, just a black image.
Turns out I can see the objects with a basic minimal lighting.
The only case similar to this one that I'm aware of, is in C4D which comes with a default light when no lights are in the scene.

Unless Houdini share the same default setting, I don't understand where the light comes from. Is that normal?

My set up is Mantra PBR and a Camera.

Also, I didn't figure this out yet: when I add a camera and I start orbiting/panning the viewport, Houdini automatically switches to the viewport perspective but I think I've seen orbiting the Camera (I guess with hotkeys/mouse combination).

there's an option “tie view to camera” in the viewport upper right drop down list (the one where you select the light“

In the mantra node there's an option ”Headlight creation" (under the Objects tab) which is on by default.

There is an option in the mantra pbr node called “headlight creation” under the objects tab. It creates a headlight if there are no lights in your scene. Disabling this option should solve your problem.
As for the camera, you should use the lock icon next to the viewport in order to lock camera to the viewport so you can navigate through the camera.

Thank you both!

I think I was expecting to be black because in the Help I read:

If you don’t have lights in the scene the render will come out black.

God, thank you! I was wondering about there still being light in my scene in Solaris, for about an hour. This should be OFF by default, if you ask me: KARMA - go to "Rendering", "Geometry and Shading", "Shading", turn off "Automatic Headlight Creation".

PWel
This should be OFF by default, if you ask me: KARMA - go to "Rendering", "Geometry and Shading", "Shading", turn off "Automatic Headlight Creation".

Why do you think it should be off? Without any lights, what's the point of an entirely black render? The automatic light creation is there as a convenience feature to preview your scene before you start the actual lighting process.

This way you don't need to create and position a light just for a scene preview, which makes more sense as a default. Once you create any light, that setting is ignored. Even if all your lights are set to zero intensities, that setting is ignored.

Ooooh, that's pretty clever from Houdini.

As I am fairly new to Houdini, I didn't know that this is automatically being deactivated and thought
it worked a little like the default world lighting in Blender which you manually have to turn off each time.

Thanks for bringing this to my attention.

Another proof of how Houdini is VERY smart about everything and only stupid if you (aka. ME) are.

If you want to change the default settings of a node on creation you can put the node down, choose the settings you want, select the gear at the top of the settings panel and select "set as permanent factory defaults" or something along the lines of that