Spotlight Distribution and light source visibility

[AWOLism]

Hi!

I'm playing around with the handy Spotlight Distribution node, but I'm running into a problem where bringing the Cone Angle down makes the light source disappear.
As can be seen in the screenshots, at a certain cone angle value the light rectangle stars getting covered up, until it disappears completely.

How can I avoid this, if I want the light source to still be seen?

Thanks
Andreas

[jayroth2020]

I have reported this to the dev team.

[AWOLism]

I have reported this to the dev team.

Thanks mate!

[AWOLism]

Hello Otoy team!

This appears to still be broken. Any news on when it might get fixed?

Cheers
Andreas

[karl]

Hi Andreas,

This isn't a bug - the spotlight only shines light within the cone angle specified, and if the camera isn't within the cone, no light will be sent toward the camera. The camera is just like any other part of the scene in this regard.

If you want to see the light source then some light needs to travel directly from the light source to the camera. I'm not an artist so I'm not sure what the best way to set this up would be - you could for example have two spotlights, where one of them is much dimmer but with a much wider cone angle.

[AWOLism]

Hi Karu!
Thanks for the reply.

Ok, what you are saying makes sense I guess (I'm an artist, not a developer)
But it still looks very weird to me when the visible light source plane becomes completely black, or as in the middle example in the picture I posted, when you get a very hard cut off line. Is that really physically correct?
And I wish there was an option to keep it visible, even though it may be breaking the physics, so not to have to mess around with double light sources.

Cheers
Andreas

[elsksa]

Ok, what you are saying makes sense I guess (I'm an artist, not a developer)
But it still looks very weird to me when the visible light source plane becomes completely black, or as in the middle example in the picture I posted, when you get a very hard cut off line. Is that really physically correct?

The matter of "physics" is rather off-topic. The emitted light remains plausible. Only the mesh-light surface has this appearance.
As far as I can remember, It's like that in most other renderer that uses this approach. Nothing to worry about and is to expect (and not a bug).

Do keep in mind that it is a shading based spotlight. Real lighting equipment in reality (COB LED, HMI, Tungsten, etc) are using physical accessories such as an optical projector, barn doors, etc... to control the beam angle and whatnot.

[AWOLism]

Yeah, I understand, and while it is probably standard behaviour and plausible, and that real world light equipment use barn doors etc, I will stand by my point regarding the convenience of being able to control the visibility of the source.
It would simply be nice to have the option of keeping it visible without resorting to workarounds like setting up multiple lights etc. Just my opinion.

[karl]

Is that really physically correct?

If (and that's a big if) you have a light source that only emits in a cone, and produces no light whatsoever outside the cone, then yes, it's physically correct that you can't see the light source when your eye is outside the cone.

However I don't think there are many light sources like that in the real world. A flashlight, for example, must emit some light at near 90 degrees, because you can see it from that angle, even if your face is not illuminated. The key is that if you can see the light, your face (or camera) must be being illuminated at least a little bit. So if you want to see the light source at all angles, it needs to radiate at least a little bit of light in all directions.

So the lack of realism here is caused by the spotlight distribution not matching what you get from most real light sources, rather than the actual lighting calculations in the renderer being incorrect. You would see a result like this in the real world if the light source was a lightbulb inside a long tube coated with vantablack, or something.

There's no easy way to just control the visibility of the light source, because Octane only simulates the physical behavior of light - if there is no light coming to the camera from a certain direction, the corresponding pixels can only end up black. The solutions are to either make the light source emit some light towards the camera, or to add the light source in post.

[elsksa]

The closest to reality would be to model a light and the physical accessories and/or optical elements to reproduce the emission direction, not being as "computer-precise" as what Octane does (for simplification sake as karu described).

It is important to keep in mind that offline rendering (as well as online aka game/real-time engines) is always a simplification of the highly intricate aspect of reality.