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Table of contents
Active Effects
Most parameters are common to all light types. Some parameters are limited to specific light types.
Controls whether a spot or directional light casts ground shadows during hardware shading (WindowDisplay > Hardware Shade
). If is , the become available. The default setting is .
The type of glow that the light produces when viewed directly. A light without glow can illuminate objects when the scene is rendered; however, a light needs glow to be seen by the camera when the scene is rendered. You can assign glow to all types of light except ambient lights.
If is set for a light, the , , and parameters become available. The default setting is .
No glow Glow slowly diminishes from the center of the light Glow quickly diminishes from the center of the light Glow diminishes faster towards a distance (from the light center) specified by the glow value Lower wavelengths (red) refract (or spread) more than the higher frequencies (blue) Simulates refraction due to water droplets in air. The glow value determines the radius of the rainbow. 
The type of halo that the light produces when viewed directly. is like , except that the falloff is more gradual and different falloff types are available.
The value must be greater than zero for the setting to have any affect. The default setting is .
No halo Halo slowly diminishes from the center of the light Halo quickly diminishes from the center of the light Halo diminishes faster towards a distance (from the light center) specified by the halo value Simulates a bright light source illuminating the surfaces of several camera lenses. The intensity of the flare is determined by the halo value. The size of the flare circles is relative to the field of view of the camera. Forms a circular ring with a soft central glow. The size of the ring is determined by the halo value. 
The type of fog that the light appears to be shining through. You can assign fog to point lights and spot lights to simulate light scattered from either a sphere of fog (for point lights) or a cone of fog (for spot lights). The default setting is .
No fog Fog slowly diminishes from the center of the light Fog quickly diminishes from the center of the light Fog diminishes faster towards a distance (from the light center) specified by the fog value provides sharper thresholds at the edge when the fog value is non-zero. In spot lights, the value determines how fast the light falls off from the center of the light. Shadows can be cast into volumes of fog by using spot lights when are set and the type is .
Use fog to simulate effects such as smoke or fog in the air. Light scatters diffusely and creates a radiance around light sources. This type of radiance fills a volume of space, and can show shadows of objects. Objects can immerse into the glow or stand in front of it, unlike retinal glow, which is always in front of objects. Fog glows can be visible even if the light source is totally obscured.
Use fog to simulate illuminated fog. Smoky fog can be simulated by using the 2D Noise parameters (this noise is also available for glow). The smoke can be animated by using the u and v offset parameters. Dark smoke can be specified by using the opacity parameter and making the color of the light black or negative.
Note the following when using fog:
- Fog glow is 3D: a cone for spot lights and a sphere for point lights. The camera can fly though fog glow.
- If shadowing is on for shadow casting spot lights, the fog glow displays the proper shadowing. For example, if the spot light shines through a trimmed hole, then the glow assumes the shape of the hole.
- Objects cast shadows into the volume of the fog. This can cause striking effects when combined with the 2D noise and glow effects.
For example, imagine the light on a police car in fog. As the light cuts through the smoke, objects cast shadows into the fog. When the light is pointing towards the camera a flash occurs (glow for spots only occurs when the eye is inside the spot light cone). The flash can have star and perhaps lens flare effects. The only animation needed to accomplish this is rotating the spot light.
Simulates a bright light source illuminating the surfaces of several camera lenses. The intensity of the flare is determined by the halo value. The size of the flare circles created is relative to the field of view of the camera. The parameter is not available for ambient lights. The default setting is .
Common Light Parameters
Light Type Parameters
The are different for each light type. Only the parameter is common to most light types.
Controls how quickly light intensity decreases with distance. The setting has no effect at distances less than 1 unit.
The parameter works differently for volume lights (see Decay). Valid settings are 0, 1, 2 or 3. The default setting is 1.
no decay; light reaches everything light intensity decreases directly (linearly) with distance (slower than real world light) light intensity decreases proportionally with the square of distance (the same as real world light) light intensity decreases proportionally with the cube of distance (faster than real world light)
Ray Tracer Soft Shadows
Makes the light produce soft shadows during raytracing.
The nature of soft shadows which are created is determined by the distance of the light from the object casting shadows combined with the value. Shadows are generated to match a globe shaped light with the specified radius (in world space units). If the light source is small or far away, hard-edged shadows will result. Shadows become softer-edged as the light's radius increases, as happens in the real world. However, because of super-sampling, the region of partial shadow (penumbra) can become noisy. To correct this, increase the number of samples, adjusting either the value (on light) or the global anti-aliasing level.
If you use a blending function, can be useful even when the value is 0 and the value is 1. This method helps avoid jagged shadow boundaries.
Glow
The parameters control the appearance of the light’s glow, and are only available when is set (that is, not ) under .
The strength of two-dimensional noise applied to the glow. The noise is generated on a plane that is centered at the location of the light and always oriented towards the camera. The slider range is 0 to 1. The default value is 0.
To create the illusion of illuminated smoke around a glowing light source, set the value to about 0.5 and slowly animate the and values. The smoke will appear to slowly drift by the light.
Generally fog illumination ( under ) is better than glow for creating smoke and fire effects, because fog is a 3D effect (for example, glow 2D noise cannot be occluded by objects).
Fog Illumination
The parameters control the appearance of the light’s fog, and are only available for point lights and spot lights when is set (that is, not ) under .
The fog value has a different effect on point lights and spot lights. For point lights, it determines the size of the glowing spherical volume of fog. For spot lights, it determines how the fog brightness varies across the spot light beam. A high value produces fog with uniform brightness. A low value produces fog which is brighter at the center of the spot light beam. The spot light value controls how fog brightness decreases with distance from the light source. The slider range is 0 to 5. The default value is 1.
Radial Glow Effects
The parameters control the appearance of glow and fog radial effects (, , and ), and are only available when or is set (that is, not ) under .
Controls the smoothness of glow and fog radial noise (see Radial Noise). The slider range is 0 to 5.The default value is 0.5.
