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Enabled – Turns the light on and off.

Intensity – Multiplier for the light strength; this is also the light intensity in the units set by the Units parameter.

Units – Specifies the light units. Using correct units is essential when using the V-Ray Physical Camera. The light automatically takes the scene's unit scale into consideration to produce the correct result for the scale you are working with. The possible values are:

Default – The color and multiplier directly determine the visible color of the light without any conversion. The light surface appears with the given color in the final image when seen directly by the camera (assuming there is no color mapping involved).
Lumens – Total emitted visible light power measured in lumens. When this setting is used, the intensity of the light does not depend on its size. A typical 100W electric bulb emits about 1500 lumens of light.
Lm/m/m/sr – Visible light surface power measured in lumens per square meter per steradian. When this setting is used, the intensity of the light depends on its size.
Watts – Total emitted visible light power measured in watts. When this setting is used, the intensity of the light does not depend on its size. Keep in mind that this is not the same as the electric power consumed by a light bulb for example. A typical 100W light bulb only emits between 2 and 3 watts as visible light.
W/m/m/sr – Visible light surface power measured in watts per square meter per steradian. When this setting is used, the intensity of the light depends on its size.

Color – Specifies the color of the Spot Light.

Cone Angle – Specifies the angle of the light cone formed by the V-Ray Spot Light. See the Cone Angle example below for illustration. 

Penumbra Angle – Specifies the angle within the light cone at which the light begins to transition from full strength to no lighting. When set to 0, there is no transition and the light produces a harsh edge. For illustration, see the Penumbra Angle example below.

Penumbra Falloff Type – Determines how the light transitions from full strength to no lighting inside the light cone.

Linear – The light does not have any falloff. 
Smooth Cubic – The light fades in a realistic way, similar to the Inverse Square option for Decay.

Dropoff – Controls the dropoff rate of the light intensity.

Decay – Controls the behavior of the light intensity from the distance of the light source.

Barn Door – Enables or disables the barn door effect. Barn doors restrict the light cone on the four sides of the light to produce a rectangular light shape. In the real world, barn doors are four planes attached in a square around the light.

Decay Regions – Enables decay regions to be used with the V-Ray Spot Light.

Near Decay – Toggles near decay on and off. See the examples below for more information.

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

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

Far Decay – Toggles far decay on and off. See the examples below for more information.

Far Start – Determines where the fade off starts.

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

Illumination Mask – Specifies which objects to be affected by the V-Ray Spot light.

LPE Tag – Allows you to specify a string tag that can be used in a Light Path Expression to isolate the contribution from this light. See the Advanced Light Path Expressions page for more information.