As light object numbers increase, the indirect brightness of bright lights is decreased while indirect light clamping enabled - Cycles #97305

New Issue

Alaska · 2022-04-13T11:32:24+02:00

Alaska commented

2022-04-13 11:32:24 +02:00

System Information:
Operating system: Linux-5.16.0-6-amd64-x86_64-with-glibc2.33 64 Bits
Graphics card: NVIDIA GeForce RTX 3060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.54

Blender Version:
Broken: version: 3.2.0 Alpha, branch: master, commit date: 2022-04-12 21:50, hash: 9bc678969a
Worked: Blender 2.93 and older when using Branched Path Tracing.

Short description of error:
When lights are added to a scene, it ends up changing the indirect brightness of intense lights if indirect light clamping is enabled.

Here is an example scene:
This scene is mostly lit up by indirect light from a a Sun light. I have rendered the scene once, then added 32 lights inside a box where they will have no impact on the scene and rendered the scene again. You will notice in this second render that the scene is much darker. This is due to the indirect light brightness being reduced due to how the indirect light clamping system interacts with this situation of many lights.
If I then change the "Indirect Light Clamp" to 0 (thus disabling it), you will notice that both scenes have the correct brightness.

	Sun Light - Indirect Clamp = 10	Sun Light + 32 lamps - Indirect Clamp = 10 - ISSUES	Sun Light - Indirect Clamp = 0	Sun Light + 32 lamps - Indirect Clamp = 0
Full Renders	{F13000832,width=100%}	{F13000839,width=100%}	{F13000836,width=100%}	{F13000843,width=100%}

Exact steps for others to reproduce the error:

Create a new file and change the render engine to Cycles.
Add a bright light (Nishita Sky World Shader works well by default).
Create a scene that is mostly lit up by Indirect Lighting from this light and place a camera looking at it.
Create a new collection.
In the new collection, add a bunch of lights to the scene (E.G. 32 Point lamps) and adjust their settings and/or position such that they should have little to no impact on the lighting in the scene. (E.G. Leave the light settings as default and place the lights inside a box where they will have no impact on the scene) Note: The brightness of the light must remain above 0 for this to work.
Render the scene with a high sample count (Turning adaptive sampling off will avoid some issues and decreasing the render resolution will result in faster renders.)
Switch to a different render slot in the image viewer. Disable the collection with the lights in it, and render the image again. Compare the results. Notice how they have very different brightnesses.
Change the Indirect Light Clamp to 0 (turning indirect clamping off) and repeat steps 6 and 7. Notice that the renders don't look different now (with the exception of noise levels).

Here is a file with steps 1-5 done for you:
#97305 - Light Clamping + many lights leads to loss of brightness.blend

**System Information:** Operating system: Linux-5.16.0-6-amd64-x86_64-with-glibc2.33 64 Bits Graphics card: NVIDIA GeForce RTX 3060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.54 **Blender Version:** Broken: version: 3.2.0 Alpha, branch: master, commit date: 2022-04-12 21:50, hash: `9bc678969a` Worked: Blender 2.93 and older **when using Branched Path Tracing**. **Short description of error:** When lights are added to a scene, it ends up changing the indirect brightness of intense lights if indirect light clamping is enabled. Here is an example scene: This scene is mostly lit up by indirect light from a a Sun light. I have rendered the scene once, then added 32 lights inside a box where they will have no impact on the scene and rendered the scene again. You will notice in this second render that the scene is much darker. This is due to the indirect light brightness being reduced due to how the indirect light clamping system interacts with this situation of many lights. If I then change the "Indirect Light Clamp" to 0 (thus disabling it), you will notice that both scenes have the correct brightness. ||Sun Light - Indirect Clamp = 10|Sun Light + 32 lamps - Indirect Clamp = 10 - **ISSUES**|Sun Light - Indirect Clamp = 0|Sun Light + 32 lamps - Indirect Clamp = 0| | -- | -- | -- | -- | -- | |Full Renders|{[F13000832](https://archive.blender.org/developer/F13000832/Sun_Light_-_Indirect___10.jpg),width=100%}|{[F13000839](https://archive.blender.org/developer/F13000839/Sun_Light__32_Lights_-_Indirect___10.jpg),width=100%}|{[F13000836](https://archive.blender.org/developer/F13000836/Sun_Light_-_Indirect___0.jpg),width=100%}|{[F13000843](https://archive.blender.org/developer/F13000843/Sun_Light__32_Lights_-_Indirect___0.jpg),width=100%}| **Exact steps for others to reproduce the error:** 1. Create a new file and change the render engine to Cycles. 2. Add a bright light (Nishita Sky World Shader works well by default). 3. Create a scene that is mostly lit up by **Indirect** Lighting from this light and place a camera looking at it. 4. Create a new collection. 5. In the new collection, add a bunch of lights to the scene (E.G. 32 Point lamps) and adjust their settings and/or position such that they should have little to no impact on the lighting in the scene. (E.G. Leave the light settings as default and place the lights inside a box where they will have no impact on the scene) Note: The brightness of the light must remain above 0 for this to work. 6. Render the scene with a high sample count (Turning adaptive sampling off will avoid some issues and decreasing the render resolution will result in faster renders.) 7. Switch to a different render slot in the image viewer. Disable the collection with the lights in it, and render the image again. Compare the results. Notice how they have very different brightnesses. 8. Change the `Indirect Light Clamp` to 0 (turning indirect clamping off) and repeat steps 6 and 7. Notice that the renders don't look different now (with the exception of noise levels). Here is a file with steps 1-5 done for you: [#97305 - Light Clamping + many lights leads to loss of brightness.blend](https://archive.blender.org/developer/F13000842/T97305_-_Light_Clamping___many_lights_leads_to_loss_of_brightness.blend)

Alaska commented

2022-04-13 11:32:24 +02:00

Added subscriber: @Alaska

blender-admin commented

2022-04-13 11:32:24 +02:00

#73328 was marked as duplicate of this issue

Alaska changed title from ~~Lights in a scene lead to incorrect brightnesses for World Shaders and Sun Lights when Indirect Clamping is enabled - Cycles~~ to Adding lights in a scene lead to decreased brightness for World Shaders and Sun Lights when Indirect Clamping is enabled - Cycles

2022-04-14 02:49:29 +02:00

Brecht Van Lommel commented

2022-04-14 04:24:47 +02:00

Added subscriber: @brecht

Brecht Van Lommel commented

2022-04-14 04:24:47 +02:00

Changed status from 'Needs Triage' to: 'Archived'

Brecht Van Lommel closed this issue

2022-04-14 04:24:47 +02:00

Brecht Van Lommel commented

2022-04-14 04:24:47 +02:00

This is how clamping works. If you add more lights the samples will be noisier, which means more light will be clamped out.

Ideally the sampling would be smarter so more lights don't add noise, but it's not a bug.

This is how clamping works. If you add more lights the samples will be noisier, which means more light will be clamped out. Ideally the sampling would be smarter so more lights don't add noise, but it's not a bug.

Alaska changed title from ~~Adding lights in a scene lead to decreased brightness for World Shaders and Sun Lights when Indirect Clamping is enabled - Cycles~~ to As lights objects increase, the indirect brightness of bright lights is decreased with indirect light clamping enabled. - Cycles

2022-04-14 07:10:05 +02:00

Alaska changed title from ~~As lights objects increase, the indirect brightness of bright lights is decreased with indirect light clamping enabled. - Cycles~~ to As light object numbers increase, the indirect brightness of bright lights is decreased while indirect light clamping enabled - Cycles

2022-04-14 07:12:22 +02:00

Alaska commented

2022-04-14 07:12:25 +02:00

The report was updated to be a bit more clear. This is simply for people who discover this report during searches or need to reference it in future reports about similar issues.

Alaska commented

2022-05-07 03:53:47 +02:00

Added subscribers: @cubimation, @EAW, @mano-wii, @MarcinTwarowski

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As light object numbers increase, the indirect brightness of bright lights is decreased while indirect light clamping enabled - Cycles #97305