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Comment: added env fog link

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Photometric lights utilize an .ies file containing the light's distribution profile. An .ies file contains complete specifications of a real-world light bulb or tube, including the shape of the light's cone and the steepness of the light's falloff. The manufacturer of the real-world bulb usually provides such files, and the information in those files, gathered through lab experiments, is highly accurate in its representation of the light source. By loading an .ies file, the light's properties are recreated within Blender and used by V-Ray during rendering.

IES lights are handy for architectural interior renderings, where it can be essential to accurately represent the use of specific man-made light sources in the scene. 


How to Set Up

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Certain parameters are only available as node inputs for the Light IES. For optimal editing, open the light in the V-Ray Node Editor. Follow these steps to see all the parameter locations for this node:

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  • Select the light and switch to the Shader Node Tree in the V-Ray Node Editor
  • Click on the Use V-Ray Light Nodes button that appears in the Node Editor toolbar
  • This creates the Light IES node in the V-Ray Node Editor. To adjust your view, use the middle mouse button to zoom in and pan.
  • You can now find all parameters associated with the Light IES node. Some are located on the node itself as input sockets. The rest can be found both in the Node menu in the V-Ray Node Editor right-hand panel and the Data tab.



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The render engine needs to be set to V-Ray for the V-Ray options to appear in the user interface.

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Click on the GIF to view it in full-size


Node Input Sockets

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This section describes the input sockets of the node. Some sockets have dedicated parameters, which are further described below, and some sockets are just inputs.


Transform – Allows a V-Ray Matrix node to be connected to determine the rotation and scale of the light.

Pivot Offset – Allows a vector-outputting node to be connected to control the pivot of the light. Alternatively, they can be set manually.

Color (input socket) – Overrides the Color parameter and allows a node to determine its color value.

Filter Color (input socket) – Overrides the Filter Color parameter and allows a node to determine its color value.

Shadow Color (input socket) – Overrides the Shadow Color and allows a texture to be connected to control that property.

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General

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Enabled – Turns the light on and off.

Color mode – Color Mode – Determines how the color of the light is controlled, either Color or Temperature.

Color – Controls the color of the light. When using photometric units, this color is normalized so that only the color hue is used, whereas the Power parameter determines the light intensity.

Temperature –  – When the Color Mode is set to Temperature, this parameter controls the color of the light by degrees Kelvin.

IES File – Load an .ies file to use for the current light.

Filter Color – A multiplier for the Color parameter of the light. This option is not available with V-Ray GPU.

Power – Determines the intensity of the light. The default value of 0 means the light intensity comes only from the .ies profile. If a value different than 0 is used, that number is taken as the light intensity instead. A reasonable number would be in the range of 500-1000. The value is in lumens.

Override Prescribed Power – Overrides the power specified in the file if > 0. The value is in lumens.

Rescale Max Intensity – The IES file's default global light intensity is multiplied to match the user's defined light intensity.

New Max Intensity – Specifies the strength of the light as a multiplier when Rescale Max Intensity is enabled.

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Options

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

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

Affect Atmospherics – When enabled, the light influences the atmospheric effects in the scene. This option is not available with V-Ray GPU.

Diffuse Contribution – Specifies a multiplier for the effect of the light on the diffuse.

Specular Contribution – Specifies a multiplier for the effect of the light on the specular.

Atmospherics Contribution – Determines the amount of influence the light has on the atmospheric effects. This option is not available with V-Ray GPU

Area Speculars – When enabled, the specular highlights are computed with the real light shape, as defined in the .ies files. For this to work, you also have to enable Soft Shadows. When this parameter is disabled, the specular highlights are computed using a point light approximation instead of the real shape. This option is not available with V-Ray GPU.

LPE Label – Allows a label to be assigned, which can be used to reference the light in a Light Path Expression. This is especially useful when working with the Light Select render element to evaluate custom light contribution in the scene.

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Shadows

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

Shadow Color – Controls the color of shadows for the light. Note that anything different from black is not physically correct. This option is not available with V-Ray GPU.

Shadow Bias – Moves the shadow toward or away from the shadow-casting object. Higher values move the shadow toward the object, 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.

Soft Shadows – Sometimes, the .ies file contains information about the physical shape and size of the bulb. When this option is enabled, the light casts shadows according to this information. Otherwise, the light casts shadows as if it were a Point Light.

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Photon Emission

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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.

Caustics Multiplier – This value is 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 settings.

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Sampling


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This rollout is not available with V-Ray GPU.

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 from the light; lower values make the light range larger. If you use 0.0, the light is calculated for all surfaces.

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Decay

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The Decay parameters determine how the light fades in and out. The Near Decay determines Decay determines how light fades in. The light isn't at its maximum value at its source , but instead gradually increases until it reaches the the Near end. The Far Decay determines End. The Far Decay determines how light fades out. The light isn't at its maximum value at its end , but instead gradually decreases after the Far startStart.

Decay The decay option is useful for creating hotspots or controlling the length of a "God Rays" effect created with Environment Volume Fog. 


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Near Decay On – Toggles near decay on and off.

Near Decay Start – Determines where the fade in starts. Anything before this point is rendered dark.

Near Decay End – Determines where the fade in ends. After this threshold, the light is at its full value.

Far Decay On – Toggles far decay on and off.

Far Decay Start – Determines where the fade off starts.

Far Decay End – Determines where the light reaches a value of 0, i.e. completely fades off. 

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Light Shape

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IES Light Shape – Determines the shape of the light when calculating Soft Shadows. By default, the V-Ray IES Light uses the shape information stored in the .ies file. Overrides for the light shape can be specified from the list below.

From IES File
Point 
Rectangular
Circular
Sphere
Vertical cylinder
Horizontal cylinder oriented along lum. length
Horizontal cylinder oriented along lum. width
Ellipse oriented along luminaire length
Ellipse oriented along luminaire width
Ellipsoid oriented along luminaire length
Ellipsoid oriented along luminaire width
Elliptic cylinder
Hor. elliptic cylinder along lum. length
Hor. elliptic cylinder along lum. width
Vertical Circle
Vertical Ellipse
Cuboid

Width – Specifies the width for applicable Light Shape types.

Length – Specifies the length for applicable Light Shape types.

Height – Specifies the height for applicable Light Shape types.

Diameter – Specifies the diameter for applicable Light Shape types.

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