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This infinite light simulates a bright distant light source like from the sun or moon. This light bathes the entire scene and treats the light as-if the rays are parallel by default (this can be altered in the settings below).
Only rotation (direction) will be applied. Translation and scaling of this light will be ignored.
You will see mention of "non-physical" controls. These controls are designed to help artists make art-directed imagery by ignoring certain laws of physics we usually simulate.
IntensityScales the contribution of this light linearly. The light intensity is computed using physical units. The default light begins at a high value of 50000.0. Below we also have 10000 and 90000.
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. Below shows values -1.0, then 0.0, and finally 1.0.
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. Below are the default of 0.53, 5.0, and then 10.0. 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.
The color of the emitted light.
Turns color temperature on or off. Below we use the following temperatures: 6500K (default), 4000K, and lastly 8500K.
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).
The effect will be less pronounced on fully saturated mono-chromatic lights. Defaults to 6500K, which should be very close to white on most monitors (D65 illuminant used by sRGB and Rec 709).
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.
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. Below we go from default (1.0) to 0.15 and then 0.0 (no contribution). This scene has subtle reflections but you can notice the light disappears from the reflection in the chrome ball far right.
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. Below we go from default (1.0) to 0.5 and then 0.0 (no contribution)..
All shadow parameters will be ignored if the light's Trace Light Paths is enabled in Advanced. The below options are all non-physical controls when used out of their default state. If Trace Light Paths is enabled then their physical nature is enforced.
Enable raytraced shadows. Below is on (default) and off.
The color of the shadows cast by emitted light. Below there's Red, Yellow, and Blue-Green.
.0 0.0 0.0
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.
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. From the left we have Off, 1.0 and then 0.15. 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. The default is 1.0 and shown here first, then 0.5 and finally 0.1.
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.
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 PxrUPBP Integrators.
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.
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.
Specify the light group name used for light group LPEs. This is useful to generate per-light AOVs for later adjustment in compositing.