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.

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

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.

Exposure#

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

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 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

Texturing Light Contribution with a scope and a default texture

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

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.

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.

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.

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.

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:

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:

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:

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:

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

Direct Path Weights#

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

Indirect Path Weights#

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