VRay for 3ds Max Manual

VRayLight Parameters

	General
	Parameters
		General
		Intensity
		Size
		Options
		Sampling
		Texture
		Dome light options
		Mesh light options
	Notes

General

The VRayLight is a V-Ray specific light source plugin that can be used to create physically accurate area lights.

Parameters

General

On - turns the VRayLight on and off

Exclude - allows one to exclude objects from being illuminated or from shadow-casting for the light.

Type - specifies the shape of the light:

Plane - the VRayLight has the shape of a planar rectangle.

Sphere - the VRayLight has the shape of a sphere.

Dome - the VRayLight acts like the SkyLight object in 3ds Max. The light is coming from a (hemi)spherical dome above the z-axis of the light.

Mesh - allows the usage of any triangle mesh as the shape of the light. If the light is close to other surfaces in the scene, it is best to use this mode with GI enabled. This will allow V-Ray to use combined direct and GI sampling of the mesh light for best results. Without GI, the light may produce noisy results for surfaces that are very close to it. Currently there are some restrictions when using mesh lights; refer to the Notes section below.

Intensity

Units - allows choosing the light units. Using correct units is essential when you work with the VRayPhysicalCamera. 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 (image) - 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).

Lumious power (lm) - 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.

Luminance (lm/m^2/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.

Radiant power (W) - 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 a light bulb for example. A typical 100W light bulb only emits between 2 and 3 watts as visible light.

Radiance (W/m²/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.

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  light Multiplier.

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

Size

Half-length - the half-length of the light source, measured in scene units. If Sphere light source is selected this value corresponds to the sphere's radius. This parameter is ignored for Dome lights.

Half-width - the half-width of the light source, measured in scene units. This field has no effect when Sphere or Dome light source is selected.

W size - currently this parameter does nothing. It's reserved if (one day) the VRayLight supports box-shaped light sources.

Options

Cast shadows - when on (the default), the light casts shadows. Turn this option off to disable shadow casting for the light.

Double-sided - when the light is a planar light source this option controls whether light is beamed from both sides of the plane. This field has no effect for Sphere or Dome light sources.

Invisible - this setting controls whether the shape of the VRayLight 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 option.

Ignore light normals - normally, the surface of the source emits light equally in all directions. When this option is off, more light is emitted in the direction of the source surface normal.

No decay - 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). When this option is on the intensity will not decay with distance.

Skylight portal - when this option is on, the Color and Multiplier parameters are ignored; instead the light will take its intensity from the environment behind it.

Simple portal - this option is only enabled if the Skylight portal option is on. It tells the VRayLight 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 this option is on and GI calculation is set to Irradiance map V-Ray will calculate the effects of the VRayLight 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 - this determines whether the light is affecting the diffuse properties of the materials.

Affect specular - this determines whether the light is affecting the specular of the materials.

Affect reflections - this determines whether the light will appear in reflections of materials.

Sampling

Subdivs - this value controls the number of samples V-Ray takes to compute lighting. Lower values mean more noisy results, but will render faster. Higher values produce smoother results but take more time. Note that the actual number of samples also depends on the DMC Sampler settings.

Shadow bias - bias moves the shadow toward or away from the shadow-casting object (or objects). If the Bias value is too low, shadows can "leak" through places they shouldn't, produce moire patterns or making out-of-place dark areas on meshes. If Bias is too high, shadows can "detach" from an object. If the Bias value is too extreme in either direction, shadows might not be rendered at all.

Cutoff - this parameter 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.

Texture

Use texture - when the Rectangle, Dome or Mesh light type is used, this tells the light to use a texture for the light 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. The texture intensity is also affected by the Multiplier of the light.

Resolution - specifies the resolution at which the texture is resampled for importance sampling.

Adaptiveness - controls the amount to which light sampling is tuned to the texture brightness. If 0.0, no adaptation based on texture intensity is performed. When set to 1.0 (the default), the maximum amount of adaptation is used. Changing this parameter may be required if there are very bright portions of the map, which are however obscured for the particular scene. This will prevent the light from concentrating a lot of samples in this area and shooting too few samples in other parts of the texture. This parameter is ignored when the light type is Mesh as in that case sampling is not dictated by texture brightness.

Dome light options

Spherical (full dome) - when on, this option causes the dome light to cover the entire sphere around the scene. When off (the default), the light covers a hemisphere only.

Target radius - for the Dome light, defines a sphere around the light icon where photons are being shot when photon-mapped caustics or the global photon map are used.

Emit radius - for the Dome light, defines a sphere around the light icon from which photons are being shot towards the target radius area.

Mesh light options

Pick mesh - click on the button to select any triangle mesh object from the scene as the shape of the light. If no mesh is specified, the light will assume a box shape.

Flip normals - if this is on, the normals of the mesh source will be inverted thus producing light on the opposite side.

Replace mesh with light - if this option is checked when you pick the mesh it will be removed and the V-Ray mesh light will be created in its place.

Extract mesh as node - use this button to restore when you have created a mesh light replacing the actual geometry with the light you can get the original geometry back by clicking on this button

Notes

• When using Mesh lights or texture-mapped Plane lights, it is best to have GI enabled. This allows V-Ray to use combined direct and indirect sampling for the light, which greatly reduces the noise for surfaces close to the light.
   
• Currently Mesh lights do not work properly if the mesh source object has motion blur. This will be implemented in a future release. Motion blur works properly for the other light types (Plane and Sphere).