Directional Area Lights

[chafouin]

I have a couple of questions about the new Area Light Spread setting as I am incorporating it into the Physical Lights units of my Photographer addon.

• The spread value conserves energy, meaning using a narrower spread will focus the beam and make it brighter. However, this is not how the Spotlight Size (cone angle) works, does it make sense to have two different behaviors? I see that you wanted to give the option but it’s not what has been committed at the moment.
  I will support both depending if it’s lumen or candela anyway, but I am curious about this choice.

• Spread is not supported by EEVEE and breaks compatibility between the two engines now, especially because of the brightness difference. Will it be added before 2.93 release?

Best,
Fabien

[brecht]

@chafouin

The spread value conserves energy, meaning using a narrower spread will focus the beam and make it brighter. However, this is not how the Spotlight Size (cone angle) works, does it make sense to have two different behaviors? I see that you wanted to give the option but it’s not what has been committed at the moment.

It makes sense to have the option for both, it just was decided this was not a requirement for the patch to be added.

@chafouin

• Spread is not supported by EEVEE and breaks compatibility between the two engines now, especially because of the brightness difference. Will it be added before 2.93 release?

Probably not for 2.93.

It’s not obvious how to do this in realtime, at least I’m not sure how you’d adapt the Linearly Transformed Cosines method to this. But that shouldn’t hold back features in Cycles.

[KarimJoseph]

hello Matteo thanks for the new feature very useful.

I have a question regarding using area lights as a projector.
I tested it with a video file and it works. However currently in order to get a sharp projection on a wall, the area light has to be close to the wall like this:

As soon as I move it away the projection gets blurry.

My guess is that it has to do with the current minimum of 1 degree spread?
Would it be possible to have the option to set it to 0, in order to use the area light as a projector?

[lsscpp]

Hi, it is already being proposed, discussed and (I guess) planned

[KarimJoseph]

ok thanks. Can you please share the link to the discussion?

[lone_noel]

It was mentioned in the rendering meeting notes from 2021-04-27:

Cycles

• […]
• Juan is working on documentation and images for light spread. He also suggest support light spread angle 0 for projectors, Brecht will add it to the list of things to improve for sampling light spread.

Link to the topic:

2021-04-27 Blender Rendering Meeting

Attendees Brecht Van Lommel (Blender) Kévin Dietrich (Blender) Thomas Arcila (AMD) Brian Savery (AMD) Patrick Mours (NVIDIA) Sergen Eren (Tangent) Juan Gea Rodriguez Notes Cycles Cycles X announcement and tasks on developer.blender.org: #87839 - Cycles X - New Features and Changes - blender - Blender Projects #87837 - Cycles X - Restoring Features - blender - Blender Projects #87836 - Cycles: GPU Performance - blender - Blender Projects The announcement that the OpenCL rendering kernel…

[matteolegna]

The current model “goes crazy” with spread values very close to 0 (number of rays hitting the light approaching zero, while their individual intensity skyrockets towards infinity), that’s the reason behind the decision of capping it to 1 degree. I would personally be very committed to making it work for spread 0, but I’m overwhelmed with work for at least the whole next month. Hopefully, someone will be able to get it done sooner, otherwise it is on my to-do list for sure (given that the problem is not above my skills and I’ll be able to crack it).