VRay IES Light
The VRay IES Light is a V-Ray specific light source plugin that can be used to create physically accurate area lights.
Enable - turns the VRayLight on and off
Filter Color - specifies the color of the light.
Power - this value determines the power of the light in Lumens.
File - specifies the .ies file that defines light distribution.
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.
Area Specular - if enabled, the hilights will match the shape of the light. If false, hilights will always be calculated as from a point light.
Cutoff Threshold- 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.
Photon Subdivs- this value is used by V-Ray when calculating the Global Photon Map. Lower values mean more noisy results, but will render faster. Higher values produce smoother results but take more time.
Caustic Subdivs- this value is used by V-Ray when calculating Caustics. Lower values mean more noisy results, but will render faster. Higher values produce smoother results but take more time.
Shadows - when on (the default), the light casts shadows. Turn this option off to disable shadow casting for the light.
Soft Shadows - if on, this causes the light to take into account the information about the light shape in the IES file (if there is any shape defined) so that it produces proper soft shadows.
Shadow Color - this parameter specifies a shadow color for this light. Note that any other color than black is not physically correct.
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.
Shadow 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.