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This page provides information on the BRDFLight material node.

Overview

The BRDFLight material is a special material provided with the V-Ray renderer. This material is generally used for producing self-illuminated surfaces. This material's light emission can be used as indirect as well as direct illumination in the scene.

This allows for light sources of any shape, and may even be assigned at the object level and at the face level for self-illuminating only portions of a mesh.

V-Ray for Houdini > V-Ray Light > Hou19_VRay5_Light_Material.jpg

Parameters

Light Color – Controls the color of the light material.

Color Multiplier – A multiplier for the Light Color. For more information, see the Default Color and Multiplier Values example and the Textures example below.

Transparency – A texture to use as transparency for the material. Note that making the material more transparent does not affect the intensity of the self-illumination color. This is so that you can create perfectly transparent materials that still emit light.

Double-Sided – When enabled, the material is double-sided.

Emit On Back Side – When enabled, makes the object emit light from its back side as well. If this is off, the material is rendered as black on the back sides. For more information, see the Emit On Back Side example below.

Compensate Exposure – (used when rendering with the V-Ray Physical Camera) When enabled, the intensity of the material is adjusted to compensate for the camera exposure.

Multiply By Opacity – When enabled, the color of the light material is multiplied by the Transparency texture. Otherwise, the color and transparency act independently (so-called additive transparency).

Direct Illumination – When checked, all objects that have the particular V-Ray Light material applied to them, are considered mesh lights and emit direct light.

V-Ray for Houdini > V-Ray Light > Hou19_VRay6_VRayLight_parameters.png

Example: Default Color and Multiplier Values

For the examples below, the interior cube is the default BRDFLight material. The exterior cube and ground plane have the default V-Ray Material with Reflection. The rest of the scene is shaded with a basic diffuse V-Ray Material.

This scene is rendered without any direct light sources.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_ColorAndMult_mult1_noEC_noGI.png

Color Multiplier: 1.0
Compensate Exposure: off
GI: off

The image is dark except the inner cube (self-illuminated) and faint reflection on the ground. Notice there is no GI and no lights at all, so the darkness of the scene is expected.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_ColorAndMult_mult1_EC_noGI.png

Color Multiplier: 1.0
Compensate Exposure: on
GI: off

Notice the inner cube and reflections appear brighter due to the exposure compensation. The rest of the image is still black because GI is disabled.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_ColorAndMult_mult1_noEC_GI_v02.png

Color Multiplier: 1.0
Compensate Exposure: off
GI: on

With GI enabled, the outer cube and inner sphere become slightly visible. However, the image remains very dark.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_ColorAndMult_mult50_noEC_noGI.png

Color Multiplier: 50.0
Compensate Exposure: off
GI: off

The inner cube and reflections are noticeably brighter. With GI disabled, the image remains in darkness.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_ColorAndMult_mult50_EC_noGI.png

Color Multiplier: 50.0
Compensate Exposure: on
GI: off

By enabling Compensate Camera Exposure, the reflections become brighter with the current Color Multiplier value.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_ColorAndMult_mult50_noEC_GI.png

Color Multiplier: 50.0
Compensate Exposure: off
GI: on

With GI enabled, the scene receives more illumination with the current Color Multiplier value.

Move the slider to see the example renders.

Example: Textures

This example shows using the BRDFLight material with a texture in the Color slot. In order to control the strength of the light we need to adjust the value of the Color Multiplier.

For the following examples, Emit on Back Side and GI are enabled.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_TextureOrange_Mult3_EmitBack_GI.png

Color Multiplier: 3.0

A texture is connected to the Color slot. The Color Multiplier is quite low, so only the plane and the reflection on the cube are visible.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_TextureOrange_Mult30_EmitBack_GI.png

Color Multiplier: 30.0

Increasing the Color Multiplier leads to a much brighter look in the scene. Notice that now the texture approaches a white color due to multiplying the (R,G,B) values of the texture.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_TextureBlue_Mult3_EmitBack_GI.png

Color Multiplier: 3.0

Here, another texture is connected to the Color slot. Notice the VRayMtls for the surrounding walls is unchanged, but the scene looks different due to the new texture.

Color Multiplier: 30.0

Increasing the Color Multiplier leads to a much lighter look to the scene. Notice now that the texture approaches a white color due to multiplying the (R,G,B) values of the texture.

Move the slider to see the example renders.

Example: Emit On Back Side

In the examples below, the BRDFLight material is applied to the curved plane.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_EmitOnBack_mult10_GI_noDoubleSided.png

Color Multiplier: 1.0
GI: on
Emit on Back Side: off

Increasing the multiplier visibly influences the scene. Shadows appear.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_EmitOnBack_mult10_GI_DoubleSided.png

Color Multiplier: 1.0
GI: on
Emit on Back Side: on

The scene starts to gather more light with Emit on Back Side enabled.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_EmitOnBack_mult150_GI_noDoubleSided.png

Color Multiplier: 15.0
GI: on
Emit on Back Side: off

The back is still dark, but notice the blue wall receives some GI due to higher Color Multiplier value. Shadows appear more defined.

V-Ray for Houdini > V-Ray Light > Maya2016_VRayLightMtl_EmitOnBack_mult150_GI_DoubleSided.png

Color Multiplier: 15.0
GI: on
Emit on Back Side: on

The scene gathers more light with Emit on Back Side enabled. Be aware of resulting burnt areas when using the Linear type of Color mapping.

Move the slider to see the example renders.

Notes

You can use the BRDFLight material as a light source assigned to an object. Increasing the Value of the color affects the GI solution and produces more light. Note that overbright colors may look the same as pure white but the GI results are different.
If you know the photometric power of a self-illuminated object in lumens (e.g. 1700 lm for a 100-watt bulb) you can calculate the multiplier for BRDFLight material if you divide the lumens by the surface area of the object in meters, provided that the self-illuminated color is pure white.
The direct illumination options currently only work properly if the BRDFLight material material is the only material applied on the object. They do not work if the material is part of a complex material like a BRDFLayeredMtl material. This restriction will probably be removed in a future release.