The Light Select Render Element stores direct lighting information from user-selected lights in the scene.
Overview
The Light Select Render Element represents the lighting contribution from one or more user-selected lights in the scene. Each Light Select channel can output one of the predetermined contribution types like the overall direct or indirect illumination or the direct or indirect diffuse or specular contribution to the illumination. The Full mode essentially creates a Beauty render for just the included light(s). The Light Path Expression mode allows for custom contributions to be captured. See the Light Path Expressions page.
Multiple Light Select outputs can be rendered for a single scene, and lights may be included in more than one Light Select render element.
This element is similar to the Lighting Render Element. However, the Lighting element combines the effect of all lights in the scene, while the Light Select element allows for just a user-selected light or set of lights to be broken out; showing their own individual effect(s) on the scene's illumination. By using the Light Select render element, specific lights in the resulting render can be captured and adjusted (color, temperature, brightness, etc.) in a composite without the need to re-render. For example, a Light Select element for all of the backlights in a scene, an artist may adjust the backlighting in the composite, without affecting the rest of the scene's illumination.
Note: Specific objects can be excluded from this Render Element by disabling the Generate Render Elements option in the V-Ray Object Properties for the selected object(s).
UI Path: ||out Network|| > V-Ray Render Elements node > V-Ray > Render Channel > V-Ray Light Select (RE)
Attributes
Name – The text added to the end of the rendered file, when saved as a separate file (e.g. myrender.lightselect.vrimg).
Type– Sets what type of lighting contribution is generated in the element as follows:
Direct Illumination – Lighting within the Light Select element behaves as normal and contains diffuse and specular information.
Direct Raw – Lighting within the Light Select element behaves as a raw render element.
Direct Diffuse – Lights within the Light Select element output only their diffuse contribution and contain no specular information.
Direct Specular – Lights within the Light Select element output only their specular contribution and contain no diffuse information.
Full – Lights within the VRayLightSelect element provide full output for all information available in the scene such as GI, SSS, reflection, refraction, etc.
Indirect – Lights within the VRayLightSelect element output only the indirect scene lighting.
Indirect Diffuse – Lights within the VRayLightSelect element output only indirect scene lighting that originated from the diffuse contribution of the specified lights.
Indirect Specular – Lights within the VRayLightSelect element output indirect scene lighting that originated from the specular contribution of the specified lights.
Light Path Expressions – Allows capturing custom light transport paths with regular expressions.
LPE – Specifies a light path expression (LPE) string based on the OSL syntax. It can be used to filter certain light contributions.
Lights – Selects which lights will be affected by the Light Select render element.
Color Mapping – Applies the color mapping options specified in the Color Mapping tab of the Renderer tab of the V-Ray Renderer node. This option is enabled by default.
Denoise – Enables the render element's denoising, if V-Ray Denoiser render element is present.
Deep Output – Specifies whether to include this render element in deep images.
With V-Ray Next for Houdini the LPE is enabled by setting the VFH_LPE_ENABLE variable to 1. With V-Ray 5 for Houdini the LPE is enabled by default.
Common Use: Changing Lighting in Composite
Below is an example of how to use the Light Select Render Element in a composite.
For this example, the Top, Back, Left, and Right lights have been assigned a Light Select render element with the Type set to Full.
Next, the Top and Back lights have been assigned two Light Select render elements: The first element's Type is set to Direct Diffuse, and the second element's Type is set to Direct Specular. This gives a finer degree of control to allow separate tuning of each light's diffuse and specular contributions. All other lights in the scene have had their Type set to Direct Illumination.
The scene used for the images below uses quite a few lights. There are 4 area lights, a top light, a back light, a left light, and right light as well as a Dome light with an indoor factory HDR as its Dome light texture. As well as these, there are many Photometric IES lights in the environment and each space ship in the scene also has 3 Sphere lights. The examples below show how several Light Select Render Elements can be combined to give the same result as the Lighting render element, and combined with the Global Illumination render element to give the equivalent of the Total Lighting render element. This gives a fine level of control in the composite to change things such as the intensity or color tinting of only some lights at a time.
Light Select Render Examples
Light Select Top Light Full
Light Select Top Light Direct Diffuse
Light Select Top Light Direct Specular
Light Select Back Light Full
Light Select Back Light Direct Diffuse
Light Select Back Light Direct Specular
Light Select Left Light Full
Light Select Left Light Direct Illumination
Light Select Right Light Full
Light Select Right Light Direct Illumination
Light Select Light IES Lights Direct Illumination
Light Select Light Ship Lights Direct Illumination
Combined Light Select Direct Diffuse elements
(Same result as Direct Lighting)
Combined Light Select Direct Specular elements
Combined Light Select Direct Diffuse and Direct Specular elements
(Diffuse and specular contributions from all lights)
Combined Light Select passes to recreate the Lighting render element
Combined Light Select passes combined with the GI render element to recreate the Total Lighting render element
Beauty element prior to changes
IES Lights intensity increased and color changes to green
Left and Right lights intensity increased and tinted to a blueish color
Compositing Equation
The following diagram shows the compositing formula to recreate all the light in a scene in its most basic form using discrete Light Select Render elements. This can happen only when each light in the scene is accounted for in only one Light Select element for a particular mode. If any light is used in more than one Light Select pass, this equation results in a brighter lighting than intended, because duplicated lights in Light Select Render Elements contribute lighting more than once.
For Light Select to work correctly, all enabled lights need to be accounted for in a Light Select Render Element.
When the Light Select Render Element is set to Direct Illumination type, the sum of all the Light Select nodes replaces both Direct Lighting and Specular in the Back to Beauty composite.
When the Light Select Render Element is set to Direct Diffuse type, the sum of all the Light Select nodes replaces Direct Lighting in the Back to Beauty composite. Note that BRDFAlSurface Shader with sss_mix value other than the default 0, doesn't fit this equation.
When the Light Select Render Element is set to Direct Raw or Direct Specular type, the sum of all the Light Select nodes replaces their respective render elements in the Back to Beauty composite. Note that Direct Raw type replaces the Raw Direct Lighting render element if GI is disabled and there are no dome lights in use.
When the Light Select Render Element is set to Indirect type, the sum of all Light Select nodes replaces all the Global Illumination, Reflection and Refraction in the Back to Beauty composite. Note that the Indirect Diffuse type and the Indirect Specular type combined result in Indirect type.
When the Light Select Render Element is set to Indirect Diffuse type, the sum of all the Light Select nodes replaces Global Illumination in the Back to Beauty composite.
When the Light Select Render Element is set to Indirect Specular type, the sum of all the Light Select nodes replaces Reflection in the Back to Beauty composite.
When the Light Select Render Element is set to Full type, the sum of all Light Select nodes replaces the Beauty pass. Caustics are not included in the calculation of Light Select Render Element.
Notes
When using Light Select, a good practice is to have one Light Select pass for each light source in your scene. This way the Lighting element can be recreated from them, and adjusted as needed while compositing without re-rendering.
If the Light Select element Type is set to Direct Illumination, the specular contribution is added to the render element. While this is perfect for simple compositing, a better workflow is for each light to be selected for two Light Select Render Elements, one with its Type set to Direct Diffuse and another with its Type set to Direct Specular. In this way, the specular and diffuse lighting can both be controlled independently at a composite level.
- If the light source is wrong or missing, the Light Select will not be rendered.