The V-Ray Directional Light is a V-Ray specific light source plugin that can be used to create physically accurate area lights.
V-Ray Toolbar > V-Ray Lights tab > V-Ray Directional Light
Enabled () – Turns the V-Ray Directional Light on and off.
Color – Specifies the color of the light.
Intensity – Specifies the strength of the light.
Shadow Radius – Controls the size of the light. Where 0.0 is a point light, larger values produces soft (area) shadows.
Affect Diffuse – When enabled, the light affects the diffuse properties of the materials.
Affect Specular – When enabled, the light affects the specular of the materials.
Shadows – When enabled (the default), the light casts shadows. When disabled, the light does not cast shadows.
Caustic Subdivs – Used by V-Ray when calculating Caustics. Lower values produce noisy results but will render faster. Higher values produce smoother results but take more time.