Light Property Editor

| General | Shadow Map | Area | Photon

Every light posesses a basic set of properties which can be defined here. You can choose the type of light to use and define attributes such as light contribution, shadow map usage, selective, area light, and photon properties, etc. It is important to keep in mind that it is the job of the light shader (such as the default Soft Light shader) to implement the characteristics of the light source by controlling light functions such as color, spread, shadows, falloff, and so on.

General

Specifies what type of light you are editing; you can define basic light characteristics.

Light Type	Distinguishes between point lights (origin only), infinite lights (direction only), and spot lights (origin, direction, and spread angle). All light presets are dirived from these three light types.
Cone Angle	The angle in degrees of the exterior cone light. The cone defines the maximum spread of light.
Exponent	Controls the falloff of the light at a given distance. An exponent of 2 is physically correct, but other exponents can be chosen to make the light reach farther or less far than it should. An exponent of 1 means that the light energy does not fall off with distance.

Light Contribution

Generally, it is said that there are three types or components of light that contribute to the illumination of 3D objects in a scene: ambient light, diffuse light, and specular light. By default, most of the preset lights are set to produce both diffuse and specular lighting.

Ambient	Enables ambient light for the light source. Light that comes from all directions and averagely brightens the lit areas of an object's surface. Objects appear flat when lit by ambient light alone.
Diffuse	Enables diffuse light for the light source. Light that has a position in space and comes from a single direction. When diffuse light touches the surface of an object, it scatters and reflects evenly across that surface. If Specular is off, the light will appear much softer.
Specular	Enables specular light for the light source. Light which reflects more intensely along and around the angle of reflection from a surface and produces a bright spot or highlight at the point of reflection. The intensity of the specular reflection is dependent on the material the object is made of and the strength of the light source that is contributing the specular light. If Diffuse is off, the light will appear harsh and brighter.
Selective Light	Specifies whether the light is selective and whether the selected objects are included with or excluded from the light. Objects to be affected by a selective light are stored in the Associated Models group of a light. Inclusive: Illuminates only those objects selected in the Associated Models list. Exclusive: Illuminates all objects except those selected in the Associated Models list.
Allow Autokey during Navigation	Allows navigation (zooming, panning, etc.) to be keyed automatically using autokey while looking through the light in a 3D view. This works only with spotlights. For a complete description, see Autokeying Camera Navigation [Basics].

Shadow Map

Controls how shadows are created by a shadow map for the selected light.

Use Shadow Map	Activates shadow map properties.
Resolution	Specifies the resolution (in pixels) of the computed shadow map.

Render/Viewport

The Render settings are used when rendering to file or in the render region, while the Viewport settings are used in High Quality display mode.

Softness	Creates soft shadows by defining a penumbra area. The penumbra is the "secondary" shadow that is cast when only part of the light is blocked by the object.
Samples	Specifies the number of samples to be calculated. Soft shadows are produced by distributing samples in a region of the shadow map. For the viewport, this value is clamped by the environment variable XSI_HIGH_QUALITY_VIEWPORT_MAX_SHADOW_SAMPLES.

Volumic Shadow Maps

Volumic shadow maps, instead of simply storing the distance from the light to the first object hit, will raymarch through the scene from the light origin until a fully opaque object is hit. Along the way it stores the changes in color or intensity along with the depth at which the change occurred.

Volumic shadow maps are useful when rendering shadows for geometry hair.

Use Volumic Shadow Maps	Toggles volumic shadow maps.
Sub-Samples	Controls the oversampling of each pixel of the shadow map. The value specifies the size of the oversampling rectangle in N x N sub-pixels. For example, if Samples is set to 3, nine samples are taken, per shadow map pixel.
Step Size	Sets the distance between each sample taken when raymarching from the light origin.
Shadow Type	Specifies what is sampled and stored in the shadow map. Intensity Only: Only changes in intensity are stored in the shadow map, resulting in just grayscale shadows. Full Color: Changes in color are stored in the shadow map Color sampling has a higher memory overhead than just intensity sampling, but allows for full-color shadows.

Area

Contains settings that define area light options for point and spotlights. The Area Light options are available in the Light property editor.

Area Light	Activates area light properties for the selected light.
Visible in render	Makes the light-emitting surface visible in the rendered output (rendered frame, preview, render region, and so on). This is useful when you want area lights to appear in reflections. Note that the rendered area light uses the light color and intensity defined in the light shader's property editor (by default this is the Soft Light shader).
Geometry	Sets the shape of the area light source. Rectangle: Emits rays from a rectangular area. A rectangle area light is specified by two vectors that describe the lengths of the edges. The light icon appears with a rectangle around it. Disc: Emits rays from a disc-shaped area. A disc area light is specified by its normal vector and a radius. The light icon appears with a circle (disc) around it. Sphere: Emits rays from a spherical surface. A sphere area light is specified only by its radius. The light icon appears with a sphere around it. Cylinder: Emits rays from an open-ended cylindrical surface. A cylinder area light is specified by its axis and radius. The light icon appears with a cylinder around it. Cylindrical area lights are always open at both ends. Object: Emits rays from a surface defined by the shape of a geometric object in the scene. All points on its surface emit light uniformly. It is generally a good idea to keep the triangle count of the object as low as possible for maximum performance. The Samples usually have to be set much higher for object lights. User: User-defined area lights are intended for use with custom light shaders. This option allows the custom light shader to completely control all the light sampling. User-defined area lights rely completely on a specialized light shader to select sample points on the surface, cast shadow rays at those points (if required), and return the illumination from the points. These lights are treated like point lights, without origin or direction. It is the responsibility of the light shader to set the origin and direction as necessary, including any dependent values such as distance attenuation. Also, in Flat Light Mode, the Soft Light shader requires that the User option be enabled, otherwise, back faces are not lit properly.
Object	Specifies the name of the object being referenced by the area light.
Pick	Allows you to choose a geometric object in your scene that will be used to define the shape of the area light. Click the Pick button. In the pop-up explorer, select the object you want to use. Right-click outside the explorer to end the picking session. The Object text box displays the name of the selected object.

Samples

Area lights use Quasi-Monte-Carlo sampling patterns taken in the U and V directions of the light area. Each area light is sampled multiple times, therefore, the sampling level defined for the render pass can be lowered even for high-quality renders.

U, V	Specifies the number of samples taken in the U and V dimensions of the light area. The sampling pattern depends only on the product of U * V samples, and not on the individual values. The actual number of samples taken is the greatest power of 2 that does not exceed U * V samples.

Low Samples

Low UV sampling is useful when you want to optimize the amount of samples used for an area light that's illuminating a point after a given number of reflection and refraction levels. For example, when an object is being lit from behind one or more semi-transparent planes.

Level

When Level is set to 0 (zero), low UV sampling is disabled.

When Level is greater than 0 (zero), low UV sampling is used instead of UV sampling, if the sum of reflections and refractions exceeds the value set for Level.

The effect is that reflections and refractions of soft shadows are sampled at lower precision, which can improve performance significantly. This optimization does not apply to user-defined area lights because in this case the ligth shader is in control of the sampling rates, and if it gets cut off early the illumination results may not be correct.

U, V

Specifies the number of low level samples taken in the U and V dimensions of the light area. The low level sampling pattern depends only on the product of low U * V samples, and not on the individual values. The actual number of samples taken is the greatest power of 2 that does not exceed low U * V samples.

Area Transformation

Scaling X, Y, Z	Sets the size of the area light. The X value corresponds to the X axis of a rectangle or the radius of discs or spheres. The Y and Z values correspond to the Y and Z axes of the rectangle.
Rotation X, Y, Z	Performs rotation relative to the light's local coordinates in degrees. The Z axis of the local coordinates is defined by a vector from the spotlight's position to its interest's position. If this option is not selected, rotations are performed relative to the global coordinate system. Rotation has no effect when the Geometry option is set to Sphere.

Photon

Controls indirect lighting and caustic highlights.

To render caustics, you must also set the Caustic options for the objects that receive and transmit the effect, as well as activate caustics on the Photon page of the mental ray Render Options Property Editor and/or the Render Region Options Property Editor.

Caustics	Activates caustic lighting properties on the light.
Global Illumination	Activates global illumination properties on the light.

Energy

Color	Controls the color of light rays emitted by the light for the purpose of photon lighting calculations. Note that this parameter can be animated.
Intensity	Controls the intensity of the selected energy color.

Number of Emitted Photons

NoteHigh values for these parameters will greatly increase render times.

Caustic	Controls the quality of the illumination. To easily see caustic effects, boost the value to 100 000 or higher and then tune.
Global Illumination	Controls the quality of the illumination. To easily see global illumination effects, boost the value to 100 000 or higher and then tune.

Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License