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 the following categories: Light, Light Profiles, Lightmass, Light Function, Performance, and Distance Field Shadows.
Light
The Light category holds the settings you'll change most: how bright the light is, its color, the shape of its cone, and how far it reaches. It also controls how the light casts shadows and how it contributes to features such as volumetric fog, ray tracing, and MegaLights. Many of these are in the category's advanced section, which you can expand at the bottom of the category.
| Property | Description |
|---|---|
Intensity | Total energy that the light emits, in the units set by Intensity Units. |
Intensity Units | The units used for Intensity: Unitless, Candelas, Lumens, EV, or Nits. Changing the units converts the current value so the light's brightness stays the same. |
Light Color | The color that the light emits. |
Use Temperature | Whether to use Temperature to set the light's color. When disabled, the light uses white (D65). |
Temperature | The color temperature of the light in Kelvin. White (D65) is 6500 K. |
Inner Cone Angle | Sets the inner cone angle of the Spot Light, in degrees. Inside this cone the light is at full brightness. If you set it larger than the Outer Cone Angle, the outer angle increases to match. |
Outer Cone Angle | Sets the outer cone angle of the Spot Light, in degrees. The light falls off between the inner and outer cones and doesn't reach past the outer cone. When Intensity Units is set to Lumens, the light's output is spread across the cone, so narrowing the cone makes the light brighter. |
Attenuation Radius | Bounds the light's visible influence. |
Source Radius | Radius of light source shape. Larger values give softer shadows and broader specular highlights. |
Soft Source Radius | Soft radius of light source shape. |
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. |
Cast Shadows | If the light casts shadows. |
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 Attenuation Radius is only clamping the light's contribution. |
Light Falloff Exponent | Controls the radial falloff of light when Use Inverse Squared Falloff is disabled. |
Specular Scale | Multiplier on specular highlights. Use only with great care! Any value besides 1 is not physical! Can be used to artistically remove highlights mimicking polarizing filters or photo touch-up. |
Diffuse Scale | Multiplier on diffuse lighting. Use only with great care! Any value besides 1 is not physical! |
Shadow Bias | Controls how accurate the shadows from this light are. |
Shadow Slope Bias | Works with Shadow Bias to control self-shadowing accuracy, adding more bias to surfaces at a steep angle to the light. |
Shadow Resolution Scale | Scales the resolution of the shadow maps used to shadow this light. |
Shadow Filter Sharpen | How much to sharpen shadow filtering for this light. |
Contact Shadow Length | The length of screen space to ray trace for sharp contact shadows. A value of zero disables this option. |
Contact Shadow Length In World Space Units | Whether Contact Shadow Length is in world space units instead of screen space units. |
Contact Shadow Casting Intensity | Intensity of the contact shadows cast by primitives with Contact Shadow enabled. A value of 0 casts no shadow. |
Contact Shadow Non Casting Intensity | Intensity of the contact shadows cast by primitives with Contact Shadow disabled. A value of 0 casts no shadow. |
Cast Translucent Shadows | Whether this light is allowed to cast dynamic shadows through translucent objects. |
Cast Static Shadows | Whether this light casts static shadows. |
Cast Dynamic Shadows | Whether this light casts dynamic shadows. |
Affect Translucent Lighting | Whether the light affects translucency or not. |
Volumetric Scattering Intensity | Intensity of the volumetric scattering from this light, as a scale on Intensity and Light Color. |
Cast Volumetric Shadow | Whether the light shadows volumetric fog. Disabling this can save GPU time. |
Transmission | Whether light from this light passes through surfaces that use subsurface scattering profiles. Requires the light to be Movable. |
Cast Deep Shadow | Whether the light casts high quality self-shadowing on hair strands, at an extra GPU cost. |
Deep Shadow Layer Distribution | How the deep shadow layers used for hair strands are spread out, from 0 (evenly spaced) to 1 (exponential, which gives more detail on small nearby features). |
Cast Ray Traced Shadows | Whether the light casts ray traced shadows: Disabled, Use Project Setting, or Enabled. |
Affect Ray Tracing Reflections | Whether the light affects objects in ray traced reflections. |
Affect Ray Tracing Global Illumination | Whether the light affects ray traced global illumination. |
Allow MegaLights | Whether this light can use MegaLights when MegaLights is enabled in the project settings or a Post Process Volume. |
MegaLights Shadow Method | The shadowing method MegaLights uses for this light. Ray Tracing gives a fixed cost and correct area shadows. Virtual Shadow Map has a higher cost per light, but casts shadows directly from Nanite geometry. |
Lighting Channels | The lighting channels this light affects. Lighting channels apply to opaque materials, direct lighting, and dynamic lighting and shadowing. |
View Lighting Channels | Controls which views this light affects. |
Inverse Exposure Blend | Blends between the light's intensity and its intensity divided by exposure. This keeps gameplay lights at a consistent brightness as the camera's exposure changes. |
Cast Shadows From Cinematic Objects Only | Whether the light casts shadows only from components with Cast Cinematic Shadow enabled. |
Force Cached Shadows For Movable Primitives | Whether to cache shadows for movable primitives for this light, even when cached shadows are disabled for movable primitives in the project. |
Override Ray End Bias | Whether to use the Ray End Bias value on this light. |
Ray End Bias | Bias for the end of a shadow ray. Use it to fix self-occlusion artifacts between the light and nearby geometry, such as a lamp's enclosure mesh. |
Light Profiles
Light profiles use IES data, measured from real-world light fixtures, to shape how light spreads from the light. For more information, see IES 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 Intensity | If false, it will use the Intensity 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 Intensity Scale | Scale for IES brightness contribution, as they can seriously blow out a scene. |
Lightmass
These settings control how Lightmass treats this light when you build lighting. They affect only the precomputed lighting from Static and Stationary lights.
| Property | Description |
|---|---|
Indirect Lighting Saturation | A value of 0 will completely desaturate this light in Lightmass, 1 will be unchanged. |
Shadow Exponent | Controls the falloff of shadow penumbras. |
Use Area Shadows for Stationary Light | Whether to use area shadows for a Stationary light's precomputed shadow maps, which soften shadows as distance from the caster grows. |
Light Function
A light function uses a material to filter the light's intensity, for example to make a light flicker or to project a pattern. For more information, see Light Functions.
| Property | Description |
|---|---|
Light Function Material | The light function material to be applied to this light. |
Light Function Scale | Scales the light function projection. |
Fade Distance | 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, for example, beyond the Fade Distance. |
Performance
These settings fade out and stop rendering the light beyond a set distance from the camera. Use them to save the cost of lights that are too far away to make a visible difference.
| Property | Description |
|---|---|
Max Draw Distance | The distance from the camera at which the light stops rendering lighting and shadows. A value of 0 means there's no max draw distance. |
Max Distance Fade Range | The distance over which the light fades out as it approaches Max Draw Distance, so it doesn't pop. Requires Max Draw Distance to be greater than 0. |
Distance Field Shadows
These settings control ray traced distance field shadows, which use Mesh Distance Fields to cast soft area shadows with sharp contacts. They have a low cost for each object, so they work well for lights that affect many meshes.
| Property | Description |
|---|---|
Distance Field Shadows | Whether to use ray traced distance field area shadows. Requires Generate Mesh Distance Fields to be enabled in the project settings. |
Ray Start Offset Depth Scale | Controls how far ray traced shadows are offset from the receiving surface as the camera gets farther away. Larger values reduce self-shadowing artifacts on low-resolution distance fields. |
Ray Tracing
This setting controls the quality of the light's ray traced shadows, which are used when hardware ray tracing is enabled and Cast Ray Traced Shadows is on.
| Property | Description |
|---|---|
Samples Per Pixel | The number of rays traced for each pixel when this light casts ray traced shadows. Higher values give smoother soft shadows at a higher cost. |