Lights visibility with Directionality higher than 0,5

[alessandro deana]

Hi everybody,
I have an issue with the visibility of disk lights.
The more I increase the value of the Directionality, the more light looks darker in direct visibility.
If I use values under 0,5 the lights looks good, but if I set this value higher than 5,5 the light looks black.
What can I do?
I changed the radius and the numer of segments, the option "visible directly" is turned on, but I can not solve the problem.

These are some examples:
01 - directionality 0
02 - directionality 0,5
03 - directionality 0,55

[pokoy]

The behavior makes sense since light rays are focused and you can't 'see' them when you are outside of the light beam.

[alessandro deana]

Ok your answer makes sense but I think this behaviour is really strange and useless..

I agree with you, maybe if you are out of the light beam, you can not see the light directly but this is not the behaviour in real word!
It seems more like a bug...

Any other suggestion?

This is what I need:

[pokoy]

In reality, you always have some kind of geometry either emitting light or surrounding the light source - while a cg light is a pure emitter without geometry. In your case you'd need either some geometry or a transparent (with a tiny diffuse value) cap that'll catch the light and re-emit/bounce it towards the camera.

If you still think this is wrong, submit a request or a bug report and see what dev thinks about it. Actually, what you ask isn't wrong per se and might be good to have but in cg terms it is not a bug, it's just the way 3d lights are defined.

[alessandro deana]

Thank you Pokoy,
I will post it in the bug thread, just to know what admins thinks about that.
Thank you again.

[Stan_But]

It's known old bug

[Ondra]

It's known old bug

it's not a bug ;). When light is not shining somewhere, it is also not visible on camera

[Stan_But]

It's known old bug

it's not a bug ;). When light is not shining somewhere, it is also not visible on camera

ok)

[alessandro deana]

it's not a bug ;). When light is not shining somewhere, it is also not visible on camera

Ok, so it is correct what Pokoy said.
In order to acheive the same result as the reference image, I should model some reflective geometry in order to diffuse ray lights toward the camera.
I will try and let you know the result.
Thanks

[pokoy]

Or, as someone suggested in the other thread, create a plane with the shape of the light and exclude it from shadow casting, assign a LightMtl to it and disable GI contribution so it's not adding any light on top of the light itself. This will be visible from all angles then.

[alessandro deana]

Hi everybody.
I solved the problem using this last solution.
I created a disk with a LightMtl, excluding it from shadow casting, occluding lights and GI contribution.

This is the result: