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Common Lighting Attributes#

In the following section we will go through the many different lights that are available to the raytracer as well as discussing about light linking.

Most lights share a set of predefined attributes to control the illumination color, exposure, sampling quality etc...

Enable#

Set if the light is active or not. A disabled light is skipped from rendering.

Color#

The Color attribute defines the color of the light which can also be textured. In that case, the light performs importance sample to greatly improve the quality the sampling. Please refer to Sampling Resolution for more information.

Sampling Resolution#

Sampling Resolution sets the resolution used for texture importance sampling when analyzing the input texture in order to identify bright areas. The idea is to favor sampling of areas that have most important features to improve render quality and reduce noise during light sampling.

Sampling Resolution should ideally match the resolution of the texture map so that it doesn't miss important features that should contribute to the lighting. Please note that under sampling a texture doesn't introduce noise but can change the lighting.

Note

Geometry Lights have specific attributes to control texture importance sampling. Please refer to Geometry Light section for more information.

Below are two renders of an textured Environment light using a 2048x10248 HDR probe.

Sampling Resolution 2048x1024

Sampling Resolution 16x16

When the Sampling Resolution is set to small, lighting detail of the texture can be missed out which explains why the illumination of the sun is missing here.

Tip

This attribute has no effect when no texture is connected to the color attribute of the light.

Exposure#

Exposure allows you to control the exposure of the light following this simple formula:

\[ FinalIntensity = Color * 2^{exposure} \]

Mode#

When available, the Mode attribute defines how the the intensity of the light should be computed.

  • When set to Physical the intensity of the light is computed using the total surface size of the light.
  • When in Normalized mode the light intensity is not affected by the surface of the light. While not physical, Normalized mode can be more convenient for artists since the light intensity doesn't change when the size of the light is modified.

In the renders below we scaled a default disk-shaped light

Light scaled in Normalize mode Notice how the intensity of the light is globally unchanged

Light scaled in Physical mode Notice how the intensity of the light has largely increased

Light Contribution#

Light Contribution attribute allows you to control the contribution of the light at the shaded point. Light Contribution value is multiplied to the illumination received by the shaded surface from the light.

While non-physical, Light Contribution can be very useful when used when textured with scopes for example used to adjust the intensity and color of the light in world space. It can also be used to perform some kind of light linking in texture space.

Light Contribution to white

Light Contribution to white

Texturing Light Contribution with a scope and a default texture

Texturing Light Contribution with a scope and a default texture

Using a scope to exclude the key light contribution on half the scene

Using a scope to exclude the key light contribution on half the scene

Note

It is very important to underline that Light Contribution texture space is evaluated using the shaded surface texture space. The path tracer completely ignores lights transformations. It is not meant to create gobos.

Unseen by Camera#

The Unseen by Camera attribute controls whether the light geometry is visible from the camera (primary rays).

Sample Count#

Sample Count allows to control the number of samples used for light sampling. The number of samples have a direct impact on rendering times and image quality.

A high number of samples typcially reduces the noise in the image but increases rendering time. Please note that in most cases, increasing the number of samples by 4 reduce the noise level by 2.

Noisy image resulting from an under sampled area light 16 spp

The area light is now sampled with 256 spp which result in a better looking image

Light Occlusion#

It is possible to enable light occlusion so that they are considered as a physical geometry for all types of rays.

To enable light occlusion simply toggle Enable Light Occlusion attribute.

Light Occlusion off default

Light Occlusion on note the shadow under the sphere light

Low Light Threshold#

Low Light Threshold allows you to control the value below which the evaluation of a light is skipped (considered occluded). This attribute is very useful to optimize render times in scenes with many lights as you can discards lights that almost not contributing to the image.

By default, Low Light Threshold is set to Use Renderer which uses the value set in the raytracer. You can override this value for each light in your scenes.

Low Light Threshold set to 001 rendered in 27s

Low Light Threshold set to 02 rendered in 23s Notice the suttle lack of illumination

Warning

Be careful when setting a value for Low Light Threshold. If the input value is set to high, it will introduce illumination artifacts such as early light cutoffs.

AOV Exclusive#

When enabling AOV Exclusive the light is excluded (not rendered) from the beauty, it is only evaluated on Light Path Expressions that use the token X instead of L. Please note this flag works conjointly with the light label defined by the Light Path Expression Label attribute. Please refer to Light Path Expressions for more information.

Shadow Color#

Shadow Color allows you to control the tint of the shadow per light. While this is not physical at all, it proves to be useful on some cases.

Original environment light

Same environment light with Shadow Color set to 05, 05, 05

Path Depth#

Path Depth attribute group regroups all attributes that allow you to control the visibility of lights along certain types of paths. These attributes are very useful if you want to disable light from reflections/refractions or if you want to exclude lights for direct or indirect diffuse illumination.

By default, all lights contribute to an infinite number of bounces.

Total Max Depth#

Total Max Depth allows you to set the maximum depth after which the light is considered disabled for all paths. The attribute is very useful if you want to cut the light after a certain level of recursion.

When this attribute is set to 0, it acts as if the light was disabled.

In the renders below we set Total Max Depth to 0 for the middle light:

All lights with a Total Max Depth set to Infinite

Top light with a Total Max Depth set to 0 Note the light is disabled

Diffuse Max Depth#

Diffuse Max Depth allows you to set the maximum depth after which the light is considered disabled for diffuse illumination.

When this attribute is set to 0, it acts as if the light isn't affecting diffuse.

In the renders below we change the Diffuse Max Depth of the left light:

All lights with a Diffuse Max Depth set to Infinite

Top light with a Diffuse Max Depth set to 1 The light only affects direct lighting

Top light with a Diffuse Max Depth set to 0 Note the light is reflected but doesn't contribute to diffuse

Reflections/Transmissions Max Depth#

Reflections Max Depth and Transmissions Max Depth allow you to set the maximum depth after which the light is considered disabled for reflections or transmissions.

When these attributes are set to 0, it acts as if the light isn't affecting reflections or transmissions.

In the renders below we change the Reflection Max Depth of the left light:

All lights with a Max Depth set to Infinite

Top light with a Reflections Max Depth set to 1 The light is invisible starting from the second reflection bounce

Top light with a Reflections Max Depth set to 0 The light is invisible from reflections

Shadows Max Depth#

Shadows Max Depth allows you to set the maximum depth after which the light stops casting shadows.

When this attribute is set to 0, the light doesn't cast shadows and when it is set to 1, the light stop casting shadows in secondary rays.

In the renders below we change the Reflection Max Depth of the middle light:

All lights with a Max Depth set to Infinite

Top light with a Shadows Max Depth set to 1 The light isn't casting shadows from the 1 bounce

Top light with a Shadows Max Depth set to 0 The light isn't casting shadows

Path Weights#

By default, lights are physically correct so that they all contribute the same way for each path type. However Clarisse allows extra artistic controls so that you can control the weights/intensity of lights along certain types of paths. This set of attributes is very useful if you want to reduce or boost light intensity from a specific type of paths such as diffuse, reflections, transmission etc... There are two distinct groups of attributes controlling the intensity of direct and indirect paths.

Example of paths in a path tracer

Example of paths in a path tracer

Direct Path Weights#

Direct paths are paths going from the shading point of the scene that was immediately hit by the camera ray

Attribute Description
Diffuse Weight Set the intensity of the light in direct diffuse paths.
Reflection Weight Set the intensity of the light in direct reflection paths.
Transmission Weight Set the intensity of the light in direct transmission paths.
Subsurface Weight Set the intensity of the light in direct subsurface paths.
Volume Weight Set the intensity of the light in direct volume paths.

Indirect Path Weights#

Indirect ones are the ones that are bouncing in the scene because of material sampling.

Attribute Description
Indirect Diffuse Weight Set the intensity of the light in indirect diffuse paths.
Indirect Reflection Weight Set the intensity of the light in indirect reflection paths.
Indirect Transmission Weight Set the intensity of the light in indirect transmission paths.
Indirect Subsurface Weight Set the intensity of the light in indirect subsurface paths.
Indirect Volume Weight Set the intensity of the light in indirect volume paths.

Original Render

Specular Weight at 200% Note how the reflections are stronger

Reflection Weight at 200% and Indirect Diffuse Weight at 200% It looks like there's an additional bounce