Invisible - when on, this option makes the sun invisible, both to the camera and to reflections. This is useful to prevent bright speckles on glossy surfaces where a ray with low probability hits the extremely bright sun disk.
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.
Photon Emit Distance - this parameter defines a radius around the sun from where the photons will be shot.
Photon Radius - determines the radius of the area, in where photons would be shot. This area is represented by the green cylinder around the Sun's ray vector. This parameter has effect when photons are used in the GI solutions or caustics.
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.
Affect Diffuse - this determines whether the VRaySun is affecting the diffuse properties of the materials.
Affect Specular - this determines whether the VRaySun is affecting the specular of the materials.
Diffuse Mult - a multiplier for the illumination generated by the Global Photon Map.
Caustic Mult - a multiplier for the illumination created by Caustics.
Shadows - turns the casting of shadows On and Off
Shadow 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.
Example: Shadow Bias
Enabled: on, Turbidity: 2.0, Shadow subdivision: 36, Intensity multiplier: 0.01, Size multiplier: 10.0
Shadow bias: 0.0
Shadow bias: 7.0
Shadow bias: 13.0