This page provides information on the Mesh Light.

 

Page Contents

 

Overview


The VRayLightMesh can create light sources that have volume and shape without the need to use self-illuminated objects and global illumination.

If the VRayLightMesh is close to other surfaces in the scene, it is best to use it with GI enabled so V-Ray can use combined direct and GI sampling of the mesh light. Without GI, the light might produce noisy results for surfaces that are very close to it.

 

 


Image courtesy of Leticia Reinaldo Gillett

 

 


 

UI Paths:

||V-Ray Shelf|| > (Right-click) Assign Mesh Light Properties icon > Turn selection into lights


||Create menu|| > V-Ray > Mesh lights > Turn selection into lights

 

 

Basic Parameters


 

 

 

Enabled – Determines whether or not the VRayLightMesh will emit light in the scene.

Color Mode – Sets the mode in which the color of the light will be specified.

Light Color – The color of the light. When using photometric units, this color is normalized so that only the color hue is used, whereas the light intensity is determined by the Intensity Multiplier.

Temperature – Controls the color of the light, when the Color Mode is set to Temperature.

Intensity multiplier – A multiplier for the light color; this is also the light intensity in the units chosen by the intensity units parameter.

Units – Using correct units is essential when you are working with the Physical camera Attributes. The light will automatically take the scene units scale into consideration to produce the correct result for the scale you are working with. The possible values are:

default – The color and multiplier directly determine the visible color of the light without any conversion. The light surface will appear with the given color in the final image when seen directly by the camera (assuming there is no color mapping involved). 
Lumens – Total emitted visible light power measured in lumens. When this setting is used, the intensity of the light will not depend on its size. A typical 100W electric bulb emits about 1500 lumens of light.
lm/m/m/sr – Visible light surface power measured in lumens per square meter per steradian. When this setting is used, the intensity of the light depends on its size. 
Watts – Total emitted visible light power measured in watts. When using this setting, the intensity of the light does not depend on its size. Keep in mind that this is not the same as the electric power consumed by the light source (by a light bulb, for example). A typical 100W light bulb only emits between 2 and 3 watts as visible light.
w/m/m/sr – Visible light surface power measured in watts per square meter per steradian. When this setting is used, the intensity of the light depends on its size.

 

Parameters - Texture


 


 

 

Use Texture – Allows the light to use a texture for its surface. If there are surfaces which are close to a texture-mapped light, it is best to have GI enabled. This allows V-Ray to use combined direct and indirect sampling for the light, reducing the noise for surfaces close to the light.

Texture – Specifies the texture to use. Note: If an RGBA texture file (a file that contains an alpha channel) is used, the file's alpha output must be connected to the Texture Alpha attribute to utilize the alpha channel on the light.

Texture Alpha – A multiplier for the texture's alpha channel. Note: The default value of 1 (fully opaque) remains unchanged whenever a file texture is connected to the Texture attribute, even if that file contains an alpha channel. For a file's alpha channel to be utilized, it's alpha output needs to be connected to this attribute.

Cache Texture – When enabled, V-Ray will sample the texture and produce a lower resolution one to be used for the lighting. This greatly speeds up the rendering of mesh lights with textures.

Texture Cache resolution – Specifies the resolution at which the texture is cached.

 

Parameters - Options


 


 

 

No Decay – When enabled, the intensity of the light will have no fall off with distance. Normally the light intensity is inversely proportional to the square of the distance from the light (surfaces that are farther from the light are darker than surfaces which are closer to the light). See the VRayLight page for an example of this property. For more information, see the Real-World Lights have Inverse Square Falloff example below.

Double Sided – Controls whether light is emitted from both sides of each face. For more information, see the Single-Sided vs. Double-Sided Lights example below.

Invisible – Controls whether the shape of the VRayLightMesh source is visible in the render result. When this option is turned off the source is rendered in the current light color. Otherwise, it is not visible in the scene. Note that this option only affects the visibility of the light when seen directly by the camera or through refractions. The visibility of the light with respect to reflections is controlled by the Affect specular and Affect Reflections options.

Skylight Portal – When enabled, the Color and Multiplier parameters are ignored; instead the light will take its intensity from the environment behind it.

Simple Skylight Portal – Only enabled if the Skylight Portal option is on. It tells the VRayLightMesh that there is nothing of interest behind the light itself, and so the environment color can be used directly. Normally, the portal light takes its color from whatever objects are behind it. In order to do this, the light traces additional rays, which may slow down the rendering. Turning this option on makes the rendering of portal lights faster.

Store with Irradiance map – When enabled and GI calculation is set to Irradiance map, V-Ray will calculate the effects of the VRayLightMesh and store them in the irradiance map. The result is that the irradiance map is computed more slowly but the rendering takes less time. You can also save the irradiance map and reuse it later.

Affect Diffuse – Determines whether the light is affecting the diffuse properties of the materials.

Affect Specular – Determines whether the light is affecting the specular of the materials. This means glossy reflections.

Affect Reflections – Determines whether the light will appear in reflections of materials. This means both perfect and glossy reflections.

Diffuse contribution – A multiplier for the effect of the light on the diffuse.

Specular contribution – A multiplier for the effect of the light on the specular.

 

 



 

Example: Real-World Lights have Inverse Square Falloff


The following images demonstrate the No decay parameter. In the real world, the light sources attenuate with the inverse square of the distance from the light to the shaded surface. However, you can disable light decay to achieve behavior similar to the standard Maya lights. The settings for the light source the same for both images with the exception of the Decay parameter:

 

 

No decay is off (default).

 

No decay is on.

 

 

 


 

Example: Single-Sided vs. Double-Sided Lights


This example demonstrates the difference between a single-sided and a double-sided planar area light.

 

 


Double-sided
is off.

 

Double-sided is on.

 

 

 


 

 

Parameters - Sampling






Subdivs – This parameter is disabled by default since most users will not need local control of subdivs, however, this parameter controls the number of samples V-Ray takes to compute lighting locally for this light. Lower values create more noise but render faster. Higher values produce smoother results but take more time to render. Note that the actual number of samples also depends on the Sampler settings. By default, this parameter is controlled by the Min Shading Rate in the image sampler.

To activate this parameter and specify a value, use the Use Local Subdivs parameter under the V-Ray > DMC Sampler tab in the Render Settings window.

Light cut-off threshold – Specifies a threshold for the light intensity, below which the light will not be computed. This can be useful in scenes with many lights, where you want to limit the effect of the lights to some distance around them. Larger values cut away more from the light; lower values make the light range larger. If you specify 0.0, the light will be calculated for all surfaces.

Override motion blur samples – Overrides the default number of samples that will be used to sample the current light for motion blur.

Motion blur samples – When the Override motion blur samples parameter is enabled this value will be used when sampling the motion blur created by the current light.

 

Parameters - Shadows






Shadows – When enabled (the default), the light casts shadows. Turn this option off to disable shadow casting for the light.

Shadow bias – Moves the shadow toward or away from the shadow-casting object (or objects). Higher values move the shadow toward the object(s) while lower values move it away. If this value is too extreme, shadows can "leak" through places they shouldn't or "detach" from an object. Other effects from extreme values include Moire patterns, out-of-place dark areas on surfaces, and shadows not appearing at all in the rendering.

Shadow Color – Controls the color of shadows for this light. Note that anything different from black is not physically correct.

 

Parameters - Photon Emission







Photons subdivs – Used by V-Ray when calculating the Global Photon Map. Lower values mean more noisy results, but will render faster. Higher values produce smoother results but take more time.

Diffuse multiplier – A multiplier for the diffuse photons.

Caustics subdivs – Used by V-Ray when calculating Caustics . Lower values mean more noisy results, but will render faster. Higher values produce smoother results but take more time.

Caustics multiplier – A multiplier for the generated caustics by the selected light. Note that this multiplier is cumulative; it does not override the multiplier in the Caustics rollout in the Render Settings window.


 

Parameters - Advanced Options


This option does not generally need to be changed. It is used in very specific situations.

 

 

 

Use MIS – Enables or disables Multiple Importance Sampling for the light. When MIS is enabled (the default), the light's contribution is split between direct illumination and either GI (for diffuse materials) or reflections (for glossy surfaces). This means that portions of the light's contribution will end up in the GI render elements (or the reflection render elements). When this option is disabled, the light's contribution is used for direct illumination only.

Disabling MIS might increase noise, especially in glossy reflections. Only disable this option when you have a specific reason to do so.

 

Notes


  • Each VRayLightMesh that you create has a corresponding VRayLightMeshLightLinking node created that has the name of the VRayLightMesh sufixed with the string "_lightlinking". You can use this node to perform light linking on the VRayLightMesh.