The VRay IES Light is a light source plugin that can use .ies files to create physically accurate area lights in VRay for SketchUp. It has options to control the light intensity, color, affect on materials, sampling settings, and shadows. The light uses .ies files to define the light distribution and can produce soft shadows based on the shape in the file. Settings like cutoff threshold, photon subdivs, and caustic subdivs control noise and render time.

1. VRay IES Light - V-Ray 2.0 for SketchUp Help - Chaos Group Help
http://docs.chaosgroup.com/display/VRAY2SKETCHUP/VRay+IES+Light[3/09/2015 13:37:00]
VRay IES Light Overview
The VRay IES Light is a V-Ray specific light source plugin that can be used to create physically accurate area lights.
Enable
Enable - turns the VRayLight on and off.
Intensity
Filter Color - specifies the color of the light.
Power - this value determines the power of the light in Lumens.
Options
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 highlights will match the shape of the light.
If false, highlights will always be calculated as from a point light.
Sampling
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.
Shadow
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.