Basic

Intensity

Exposure

Specifies the exposure of the area light as a power of 2. Increasing the exposure by 1 will double the energy emitted by the light source. A value of 0 produces an intensity of 1 at the source, -1 produces 0.5. Real world lighting has high energies and typical exposures are low values while you may have to type a really large number for equivalent Intensity. This is also comfortable to artists familiar with photographic measurements.

Angle Extent

Opening angle of the light source in degrees (Sun=0.53). Higher values soften the shadow edges (light rays become less parallel) while lower values make it sharper. Larger values increase shadow softness by increasing the angle of its light. Note that increasing this parameter also increases the amount of light in the scene and you may need to significantly reduce the light intensity/exposure to compensate or you may use Area Normalize to prevent changes in illumination.

Color

The color of the emitted light.

Enable Temperature

Turns color temperature on or off. Below we use the following temperatures: 6500K (default), 4000K, and lastly 8500K.

Color Temperature

Allow the user to choose the color temperature of the light in Kelvins. Unlike the basic light color, this allows the user to easily pick plausible light colors based on standard temperature measurements.This control will act like a filter or gel (a tinted transparent surface) in front of your light. If your light is white, you will get the chosen color temperature. If your light is colored, the color temperature will make it cooler (over 6500K) or warmer (below 6500K).

Primary Visibility

The light isn't directly visible to the camera by default. Turning this on makes it visible and can be written to an LPE using the emission token, 'O' This light appears as a small circle at infinite distance.

Refine

Emission Focus

Off-axis cosine power exponent to shape the emission. This controls the spread of the light.  Higher number will start focusing the light towards the center and thus narrowing the light spread. For the PxrDistantLight it will appear to dim the lighting as you increase the parameter. To alter the shadowing to appear larger/softer you should use Angle Extent.

Emission Focus Tint

Off-axis light color tint. This tints the emission in the falloff region starting from the off-angle direction of the light towards the center. By default, the tint color is black (none). For the PxrDistantLight this will tint the color of the light. Higher Emission Focus settings will increase the saturation of the chosen color.

Specular Amount

Amount of specular light that is emitted. This is a non-physical control. You could use a light with Specular Amount 0.0 to act purely as a source of diffuse light for your scene objects and avoid adding highlights. This scene has subtle reflections but you can notice the light disappears from the reflection in the chrome ball far right.

Diffuse Amount

Amount of diffuse light that is emitted. This is a non-physical control. You could use a light with Diffuse Amount 0.0 to act purely as a source of highlights for your scene objects. 

Shadows

Enable Shadows

Enable raytraced shadows. Below is on (default) and off.

Shadow Color

The color of the shadows cast by emitted light.

.0 0.0 0.0

Shadow Distance

The maximum distance of the shadow starting from the position of the point being shaded. -1.0 is unset which will use the distance between the point being shaded and the point on the light. You may use this control to artificially reduce the distance shadows are cast. This may also increase render speed by not calculating shadows outside this distance. Here it's used to remove the shadow off the back wall from the effect of the light.

Shadow Falloff

The distance from the light at which shadow falloff begins. -1.0 turns off shadow falloff. This is used along with Shadow Max Distance to create a false fade for shadows that are reduced or cut off by the Shadow Max Distance parameter. Below is an example with both parameters being used and the falloff is increased. Note this parameter may impact performance on complex lighting setups.

Shadow Falloff Gamma

The gamma of the shadow strength in the falloff zone. This requires the use of Shadow Max Distance and Shadow Falloff.

Trace Subset

Set of geometry to consider for traced shadow intersection. If this is not specified, all geometry are considered for traced shadow intersection.

Don't Trace Subset

Set of geometry to ignore for traced shadow intersection. If this is not specified, all geometry is used for traced shadow intersection.

Advanced

Normalize

When normalize is enabled, the amount of light contributed to the scene will not change as you change the angleExtent of the light source. This makes it easier to adjust highlight size without changing scene lighting.

Trace Light Paths

Enable light and photon tracing from this light. This value enforces a physically-based light and as a side-effect disables the above Shadows controls. Users may use this feature to selectively decide which lights emit photons when using the PxrVCM or PxrUnified Integrators.

Thin Shadow

Enable thin shadow and disable refraction caustics for this light. This parameter will ignored if Trace Light Paths is enabled. This is a non-physical control that creates "fake" colored shadows for transmissive objects without needing to generate photons for caustics. Below we go from On (default) to Off (opaque shadowing). Notice we lose the colored shadows and interior colored reflection choosing Off, but we gain some render speed instead.

Visible in Refraction 

Make a light visible through transmission effects like glass and windows by turning this on.

Cheap Caustics

Manifold Walk

Used with the PxrUnified Integrator and enabling Enable Manifold Walk to create inexpensive caustics. Note: You must disable Thin Shadows

Manifold Walk Exclude Group

Used with the PxrUnified Integrator and enabling Enable Manifold Walk, this trace set is ignored during manifold exploration to avoid stopping or shadowing manifold exploration rays

Light Samples

Specifies an override of the number of light samples to be taken for this light source. If set to something other than zero, it will override the sampling performed by the integrator. You might find need for this if you have unsolvable noise from this light and need more samples.

Light Group

Specify the light group name used for light group LPEs. This is useful to generate per-light AOVs for later adjustment in compositing.

Importance Multiplier

Rather than setting explicit Light Samples, users can change the amount of samples the light will be assigned internally by changing this value. RenderMan creates a set of samples at render time for all lights in the scene and changing this value rebalances the samples across the lights. Note that increasing this value will cause more samples to be selected from this light while reducing it for others in the scene. Lower than the default will decrease the samples while providing more to others in the scene.