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Rectangle Light source is visible in the resulting render. When disabled, the source light is rendered in the current light color, otherwise the light source itself is not visible in the scene.

Note: This parameter 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.

Is Disc – When enabled, the

light is in the shape of a planar disc instead of a rectangle.

Width

 – Determines the width of the light measured in scene units.

Height – Determines the height of the light measured in scene units.

Directional – When this value

is 0, the light is spread out equally in all directions. Increasing this value makes the light beam more narrow and concentrates it in one direction.

 For illustration, see the Directionality example.

Directional Preview Length – Specifies the length of the cone used to preview the Directional parameter in the viewport. This parameter is available only when Directional is greater than 0.

Directional Strength – Controls the strength of the directional distribution.

Object ID – Specifies an integer object ID to the light.

Specifies the light units. Using correct units is essential when using

the V-Ray Physical Camera. The light

automatically

takes the scene's unit 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

appears 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

does 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 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.

Color – Specifies the color of the Rectangle Light.

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.

Multiply by Color – When enabled, the Rectangle texture is multiplied by color. 

Texture – Specifies a texture to use with the light.

Color Space – Selects the color space.

Linear
sRGB

Clip By Alpha – When enabled, clips the texture based on the Alpha.

Override Alpha – When enabled, replaces the Alpha of the loaded file with the Alpha of another file. 

Alpha – Regulates the transparency of the Alpha.

Alpha Texture – Selects a Texture Alpha.

From – Replaces the Alpha of the texture with another or uses Intensity.

Resolution – Specifies the resolution at which the texture is sampled when the Texture Adaptivity option is enabled.

Adaptivity – V-Ray adjusts the number of samples taken for different parts of the texture depending on their brightness. A value of 0.0 specifies no adaptivity; a value of 1.0 specifies full adaptivity.

Illumination Mask – Specifies an additional illumination mask used to force object illumination.

LPE Tag – Allows you to specify a string tag that can be used in a Light Path Expression to isolate the contribution from this light. See the Advanced Light Path Expressions page for more information.

 – 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 Mask – Specifies

objects that cast shadows when light is directed at them.

Determines whether the light affects the diffuse properties of the materials.

Affect Specular

 – Determines whether the light affects the specular of the materials. This means glossy reflections.

Affect Reflections – Determines whether the light

appears in reflections of materials, for both perfect and glossy reflections.

Affect Atmospherics – Determines whether the light influences the atmospheric effects in the scene.

Diffuse Contribution

 – When Affect Diffuse is enabled, specifies a multiplier for the effect of the light on the diffuse component.

Specular Contribution

 – When Affect Specular is enabled, specifies a multiplier for the effect of the light on the specular component.

Atmospherics Contribution – When Affect Atmospherics is enabled, this value determines the amount of involvement.

Motion Blur Samples – Specifies the number of samples used to sample the light for motion blur.

Caustics Multiplier – Specifies a multiplier for the generated caustics by the selected object. Note that this multiplier is cumulative - it does not override the multiplier in the Caustics Tab of the V-Ray Render Settings.

Caustics Subdivs – Only used when calculating Caustics. Lower values mean more noisy results, but render faster. Higher values produce smoother results but take more time.

Cut-off Threshold – Specifies a threshold for the light intensity, below which the light

is not 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 of the light; lower values make the light range larger. When this value

is 0.0, the light is calculated for all surfaces.

Occlude Other Lights When Visible – Controls the behavior of invisible lights in relation to other light sources. When enabled, the

light blocks the lighting from other lights as if it's visible. Also in reflections the light behaves as it's visible and occludes other lights. When disabled, the light is transparent for other lights and does not occlude them. This option doesn't affect visible lights (as they always occlude other lights) and dome lights (which are always additive).

Ignore Light Normals – Usually, the surface of the source emits light equally in all directions. When this option is disabled, more light is emitted in the direction of the source surface normal.

Store With Irradiance Map – When enabled and GI calculation is set to Irradiance map, V-Ray calculates the effects of the V-Ray Rectangle Light and stores them in the irradiance map. The result is that the irradiance map is computed more slowly but the rendering takes less time. The irradiance map can also be saved for later use.