# Spot Light

## The basics of Spot Lights.

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A Spot Light emits light from a single point in a cone shape. Users are given two cones to shape the light - the Inner Cone Angle and Outer Cone Angle. Within the Inner Cone Angle, the light achieves full brightness. As you go from the extent of the inner radius to the extents of the Outer Cone Angle, a falloff takes place, creating a penumbra, or softening around the Spot Light's disc of illumination. The Radius of the light defines the length of the cones. More simply, this will work like a flash light or stage can light.

Like other lights, a Spot Light can be set to one of three Mobility settings:

• Static - (pictured left) which means that the light cannot be changed in game. This is the fastest method for rendering and allows for baked lighting.

• Stationary - (also pictured left) which means the light will only have its shadowing and bounced lighting from static geometry baked by Lightmass, all other lighting will be dynamic. This setting also allows for the light to change color and intensity in game, but, it does not move and allows partial baked lighting.

• Moveable - (pictured left) which means the light is totally dynamic and allows for dynamic shadowing. This is the slowest in terms of rendering but allows for the most flexibility during gameplay.

Two examples of a Spot Light placed inside a level are shown below demonstrating how to determine the light radius and cone effectors:

On the left a Spot Light without its cones showing light radius, on the right the same Spot Light with its cone effectors showing.

## Spot Light Properties

The properties of a Spot Light are broken up into 4 categories: Light, Light Profiles, Lightmass, and Light Function.

### Light

Property

Description

Intensity

Total energy that the light emits.

Light Color

The color that the light emits.

Inner Cone Angle

Sets the inner cone angle of the Spot Light, in degrees.

Outer Cone Angle

Sets the outer cone angle of the Spot Light, in degrees.

Bounds the light's visible influence.

Source Length

Length of light source shape.

Affects World

Disables the light completely. Cannot be set at run time. To disable a light's effect during runtime, change its Visibility property.

Indirect Lighting Intensity

Scales the indirect lighting contribution from the light.

Use Inverse Squared Falloff

Whether to use physically based inverse squared distance falloff, where AttenuationRadius is only clamping the light's contribution.

Light Falloff Exponent

Controls the radial falloff of light when UseInverseSquaredFalloff is disabled.

Min Roughness

Min roughness effective for this light, used for softening specular highlights.

Controls how accurate the shadows from this light are.

How much to sharpen shadow filtering for this light.

Whether this light is allowed to cast dynamic shadows through translucent objects.

Affect Dynamic Indirect Lighting

Whether the light should be injected into the Light Propagation Volume.

Whether this light casts static shadows.

Whether this light casts dynamic shadows.

Affect Translucent Lighting

Whether the light affects translucency or not.

### Light Profiles

Property

Description

IES Texture

The IES "Texture" used for the light profile. IES files are ASCII though Unreal represents them as textures, they are not image files.

Use IES Brightness

If false, it will use the Brightness of the light to determine how much light to produce. If true, it will use the IES files brightness in Lumens (usually much larger than default values on lights in Unreal).

IES Brightness Scale

Scale for IES brightness contribution, as they can seriously blow out a scene.

### Lightmass

Property

Description

Indirect Lighting Saturation

A value of 0 will completely desaturate this light in Lightmass, 1 will be unchanged.

Controls the falloff of shadow penumbras.

### Light Function

Property

Description

Light Function Material

The light function material to be applied to this light.

Light Function Scale

Scales the light function projection.

The distance at which the light function should be completely faded to the value in Disabled Brightness.

Disabled Brightness

Brightness factor applied to the light when the light function is specified but disabled, say from the property above: Light Function Fade Distance.

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