This page provides information on the V-Ray Rectangle Light, also known as an Area Light.
Overview
The V-Ray Rectangle Light or Area Light is a planar light source. The light shape can be set as a rectangle or a circular disk.
UI Path: ||obj Network|| > V-Ray > V-Ray Rectangle
Main
Mode – Specifies the behavior of the rectangle light.
Normal Light – Light behaves normally.
Portal – Light takes its intensity from the environment behind it. In this mode the Color and Intensity parameters are ignored.
Simple Portal – This mode can speed up rendering by simplifying the process of tracing the environment for the skylight portal. When enabled, the V-Ray Rectangle light uses all the environment color, not just the color from objects behind the light. Using just the environment behind the light requires additional rays, so using the entire environment makes the rendering of portal lights faster.
Is Disc – When enabled, the light will be in the shape of a planar disc instead of a rectangle.
Invisible – Controls whether the shape of the Dome 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.
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 Sphere Light page for an example of this property.
Double-Sided – Controls whether light is emitted from both sides of each face. See the Sphere Light page for an example of this property.
Use Intensity Texture – When enabled, allows the specification of a float texture that will override the Intensity parameter.
Intensity – Multiplier for the light strength; this is also the light intensity in the units set by the Units parameter.
U Size – Determines the width of the light measured in scene units.
V Size – 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.
Use Rect. 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 a texture to use with the light.
Color Space – 
Linear
sRGB
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.
Use Color Texture – Enables the specification of a a texture for the Rectangle Light. If used, it will override the Color parameter.
Color – Specifies the color of the Rectangle Light.
Subdivs – 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: The actual number of samples also depends on the DMC Sampler settings. By default, this parameter is controlled by the Min Shading Rate in the Image Sampler. To specify a value, enable the Use Local Subdivs parameter under the DMC tab in the V-Ray Renderer parameters.
Object ID – Specifies an integer object ID to the light.
Units – Specifies the light units. Using correct units is essential when using the V-Ray Physical Camera. The light will automatically take 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 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. With this setting is used, the intensity of the light depends on its size.
Watts – Total emitted visible light power measured in watts. With 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.
Use Global Light Level – When enabled, the light will use the global light level setting.
Shadows
Enabled – When enabled, the light casts shadows. Disable this option to turn off shadows for the light.
Use Shadow Color Texture – When enabled, allows the specification of a texture for the shadows for this light. If used, it will override the Color parameter of the Shadows rollout.
Color – Controls the color of shadows for this light. Note that anything different from black is not physically correct.
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 Mask – Specifies a texture for the shadows for this light. If used, it will override the Color parameter of the Shadows rollout.
Advanced
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.
Affect Diffuse – 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 will appear in reflections of materials, for both perfect and glossy reflections.
Diffuse Contribution – A multiplier for the effect of the light on the diffuse component.
Specular Contribution – A multiplier for the effect of the light on the specular component.
MoBlur Nsamples –Specifies the number of samples used to sample the light for motion blur.
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 of the light; lower values make the light range larger. When this value is 0.0, the light is calculated for all surfaces.
Bumped Normal Check – When enabled, the bumped normal is used to check if the light direction is below the surface.
Use Multiple Importance Sampling – Enables or disables Multiple Importance Sampling (MIS) for the light. When MIS is enabled (the default), the light's contribution is split between direct illumination on the one hand, and GI (for diffuse materials) or reflections (for glossy surfaces) on the other. This means that portions of the light's contribution will end up in the GI render elements (or the reflection render elements respectively). In certain specific situations this is undesirable and this option can be used to always calculate the light contribution through direct illumination.
GI
Store With Irradiance Map – When this option is 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.
Diffuse Multiplier – A multiplier for the diffuse photons.
Caustics Multiplier – 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.
Photon Subdivs – Only relevant when calculating the Global Photon Map. Lower values mean noisier results and faster rendering. Higher values produce smoother results but take more time to render.
Caustics Subdivs – Only used when calculating Caustics. Lower values mean more noisy results, but will render faster. Higher values produce smoother results but take more time.