Directional Lights in Unreal Engine | Unreal Engine 5.9 Documentation

The Directional Light simulates light that is being emitted from a source that is infinitely far away. This means that all shadows cast by this light will be parallel, making this the ideal choice for simulating sunlight. The Directional Light when placed 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.

Below you will see a representation of sunlight being cast through an opening in a roof.

The left image shows just the light, the right image has its Shadow Frustum enabled in order to see that the Directional Light is casting parallel light rays.

Light Direction (pictured left) is indicated by an arrow that points in the direction the light will emit which is useful for placing and orientating your light as needed.

Directional Light Properties

The properties of a Directional Light are broken up into the following categories: Light, Light Shafts, Lightmass, Light Function, Cascaded Shadow Maps, Distance Field Shadows, Atmosphere and Cloud, and Ray Tracing:

Light

The Light category holds the settings you'll change most: how bright the light is, its color, and the size of the sun disk it simulates. It also controls how the light casts shadows and how it contributes to features such as volumetric fog, translucency, and ray tracing. Many of these are in the category's advanced section, which you can expand at the bottom of the category.

Property	Description
Intensity	Maximum illumination from the light, in lux. For more information, see Physical Lighting Units.
Light Color	The color that the light emits.
Source Angle	Angle subtended by a light source in degrees. Defaults to 0.5357, which is the angle for our sun. Larger values give softer shadows and broader specular highlights.
Source Soft Angle	Angle subtended by a soft light source in degrees.
Use Temperature	When disabled, use white as an illuminant.
Temperature	Color temperature in Kelvin of the blackbody illuminant. White is 6500K.
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.
Volumetric Scattering Intensity	Intensity of the volumetric scattering from this light.
Shadow Cascade Bias Distribution	Controls the depth bias across cascades. Use this to mitigate the shadow acne difference on shadow cascades transition.
Forward Shading Priority	Forward lighting priority for the single directional light that will be used for forward shading, translucent, single layer water and volumetric fog. When two lights have equal priorities, the selection will be based on their overall brightness as a fallback.
Cast Modulated Shadows	Whether to cast modulated shadows from dynamic objects (mobile only). Requires a Stationary light with Inset Shadows For Movable Objects enabled.
Modulated Shadow Color	Color to modulate against the scene color when rendering modulated shadows (mobile only).
Shadow Amount	The amount of shadow occlusion. A value of 0 means no occlusion and no shadow.
Specular Scale	The multiplier on specular highlights. Use with care. Any values besides 1 are not physical.
Diffuse Scale	Multiplier on diffuse lighting. Use only with great care! Any value besides 1 is not physical!
Shadow Resolution Scale	Scales the resolution of shadow maps used to shadow this light.
Shadow Bias	Controls how accurate the shadows from this light are.
Shadow Slope Bias	Controls how accurate the self-shadowing of whole scene shadows from this light is. This contributes to Shadow Bias by increasing the amount of bias depending on the slope of a surface.
Shadow Filter Sharpen	How much to sharpen shadow filtering for this light.
Contact Shadow Length	Length of screen space ray trace for sharp contact shadows.
Contact Shadow Length in World Space Units	Whether to use world space units for the Contact Shadow Length.
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 to cast dynamic shadows through translucent objects.
Cast Shadows from Cinematic Objects Only	Whether the light should only cast shadows from components with Cast Cinematic Shadow enabled. This can be useful for setting up cinematic Movable spotlights aimed at characters and avoiding the shadow depth costs of the background. This option only works with dynamic shadow maps, not with static shadowing or Ray Traced Distance Field shadows.
Force Cached Shadows for Movable Primitives	Enables cached shadows for movable primitives.
Lighting Channels	Channels that this light should affect.
View Lighting Channels	Controls which views this light affects.
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.
Transmission	Whether to transmit through surfaces with subsurface scattering profiles.
Cast Volumetric Shadow	Whether to shadow volumetric fog.
Cast Deep Shadow	Whether to cast high-quality hair strands self-shadowing.
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	Sets whether to enable ray traced shadows for this light. The options are: Disabled Use Project Setting Enabled
Affect Ray Tracing Reflections	Whether to affect objects in reflections when ray-traced reflection is enabled.
Affect Ray Tracing Global Illumination	Whether to affect global illumination when ray-traced global illumination is enabled.
Allow MegaLights	Whether this light can use MegaLights when MegaLights is enabled in the project settings or a Post Process Volume. By default, MegaLights doesn't render directional lights, so this setting has no effect unless your project turns on MegaLights support for directional lights.
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.
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 an enclosure mesh.

Light Shafts

Light shafts, sometimes called god rays, add screen-space rays around the light's direction through fog and atmosphere. For more information, see Light Shafts.

Property	Description
Light Shaft Occlusion	Whether to occlude fog and atmosphere inter scattering with the screen space blurred occlusion from this light.
Occlusion Mask Darkness	How dark the occlusion masking is, a value of 1 is no darkening. Requires Light Shaft Occlusion.
Occlusion Depth Range	Everything closer to the camera than this distance will occlude the light shafts. Requires Light Shaft Occlusion.
Light Shaft Bloom	Whether to render light shaft bloom for this light.
Bloom Scale	Scales the additive bloom color.
Bloom Threshold	Scene color must be larger than this to create bloom in the light shafts.
Bloom Max Brightness	When exposure is applied, this value constrains scene color brightness.
Bloom Tint	Sets the color to tint the bloom coming from the light shafts.
Light Shaft Override Direction	Can be used to make the light shafts come from somewhere other than the light's actual direction.

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
Light Source Angle	Angle that the directional light's emissive surface extends relative to a receiver, affects penumbra sizes.
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 stationary light precomputed shadow maps.

Light Function

A light function uses a material to filter the light's intensity, for example to project the shadows of moving clouds across a level. 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.

Cascaded Shadow Maps

Cascaded shadow maps (CSMs) split the view into several shadow maps, with the most detail close to the camera. The light uses them when the project's Shadow Map Method is set to Shadow Maps. With Virtual Shadow Maps, the default for new UE5 projects, the light doesn't render cascades, so most of these settings have no effect. The dynamic shadow distance still matters, though: beyond it, only objects with Far Shadow enabled cast shadows.

Property	Description
Dynamic Shadow Distance MovableLight	How far Cascaded Shadow Map dynamic shadows will cover for a movable light, measured from the camera. A value of 0 disables dynamic shadows. If Allow Static Lighting is disabled in the project settings, this is labeled Dynamic Shadow Distance and applies to Stationary lights too.
Dynamic Shadow Distance StationaryLight	How far Cascaded Shadow Map dynamic shadows will cover for a stationary light, measured from the camera. A value of 0 disables dynamic shadows. Hidden if Allow Static Lighting is disabled in the project settings.
Num Dynamic Shadow Cascades	Number of cascades to split the view frustum into for the whole scene. More cascades give better shadow resolution, but add significant rendering cost.
Distribution Exponent	Controls whether the cascades are distributed closer to the camera (larger exponent) or further from the camera (smaller exponent).
Transition Fraction	Proportion of the fade region between cascades.
Distance Fadeout Fraction	Controls the size of the fade out region at the far extent of the dynamic shadow's influence.
Inset Shadows for Movable Objects	(Stationary lights only) Whether to use per-object inset shadows for movable components, even though cascaded shadow maps are enabled.
Far Shadow Cascade Count	The number of cascades between the dynamic shadow distance and Far Shadow Distance. Only objects with Far Shadow enabled render into them. A value of 0 means no far shadow cascades.
Far Shadow Distance	Distance at which the far shadow cascade should end.

Reusing Cascade Depths Between Frames

By default, the light renders the shadow depths for every cascade every frame. Cascades can instead reuse their depths from an earlier frame and re-render only every few frames, with the cascades staggered so they don't all update on the same frame. This lowers the cost of shadow depth rendering in projects that use Shadow Maps rather than Virtual Shadow Maps, such as projects for mobile or lower-end hardware, especially when the sun and most shadow casters don't move. The trade-off is that shadows update less often.

This option is off by default, and there's no setting for it in the Details panel or Project Settings. You control it with console variables:

r.Shadow.CSMShadowDepthReuse turns depth reuse on.
r.Shadow.CSMShadowDepthReuse.Interval sets how many frames each cascade waits before it re-renders. r.Shadow.CSMShadowDepthReuse.FarInterval sets a separate interval for the far shadow cascades.
r.Shadow.CSMShadowDepthReuse.SeparateDynamic and r.Shadow.CSMShadowDepthReuse.DynamicCascadeMask render movable objects into their own part of the shadow map for the cascades you choose, so that their shadows can update more often (r.Shadow.CSMShadowDepthReuse.DynamicInterval) than the static scene.
r.Shadow.VisualizeCSMOverlay tints the scene by cascade, which helps you see which cascade covers which part of the view while you tune these values.

Distance Field Shadows

These settings control ray traced distance field shadows, which use Mesh Distance Fields to cast soft area shadows with sharp contacts. On a directional light, they cover the distance beyond the dynamic shadow distance, which gives you cheaper shadows in the distance.

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. Enabled by default on new directional lights.
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.
DistanceField Shadow Distance	The distance at which distance field shadows end. They cover the range between the dynamic shadow distance and this distance.
DistanceField Trace Distance	How far shadows can be cast, in world units. Larger values increase the shadowing cost.

Atmosphere and Cloud

Directional Lights support the Sky Atmosphere and the Volumetric Clouds features of Unreal Engine.

Additional information and demonstration can be found in the Volumetric Clouds page under the Directional Light Interactions and Shadowing section.

Property	Description
Atmosphere and Cloud
Atmosphere Sun Light	Whether the Directional Light can interact with the atmosphere, clouds and generate a visual sun disk, all of which compose the visual sky. Enabled by default. With a Sky Atmosphere in the level, Intensity and Light Color describe the sunlight above the atmosphere, and the atmosphere dims and tints the light that reaches the ground, for example toward orange at sunset. Most of the other settings in this category require this option.
Cast Shadows on Clouds	Whether the light should cast any shadows from opaque meshes onto clouds. This is disabled for any secondary Directional Lights that have Atmosphere Sun Light enabled and set to Atmosphere Sun Light Index of 1, such as another sun or as a moon light.
Cast Shadows on Atmosphere	Whether the light should cast any shadows from opaque meshes into the atmosphere when a SkyAtmosphere is used.
Cast Cloud Shadows	Whether the light should cast any shadows from the clouds onto the atmosphere and other scene elements. The cloud shadow settings in the advanced section require this.
Cloud Scattered Luminance Scale	Scales the light contribution when scattered in cloud participating media. This can help counter balance the fact that our current multiple scattering solution is only an approximation.
Advanced Properties
Atmosphere Sun Light Index	Two atmosphere lights are supported at any time to represent the sun and moon, or two suns. Use this index to set the primary and secondary light source. For example, the sun would be 0 and the moon would be 1.
Atmosphere Sun Disk Color Scale	A color multiplied with the sun disk luminance.
Per Pixel Atmosphere Transmittance	Whether to apply atmosphere transmittance per pixel on opaque meshes instead of using the light's global transmittance.
Cloud Shadow Strength	The strength of the shadow. Higher values will block more light.
Cloud Shadow on Atmosphere Strength	The strength of shadows on the atmosphere. When set to 0, shadows on the atmosphere is disabled.
Cloud Shadow on Surface Strength	The strength of shadows on opaque and transparent meshes. When set to 0, shadows on opaque and translucent surfaces is disabled.
Cloud Shadow Depth Bias	Controls the bias applied to the front shadow depth of the volumetric cloud shadow map.
Cloud Shadow Extent	The world space radius of the cloud shadow map around the camera. Measured in kilometers (km).
Cloud Shadow Map Resolution Scale	Scales the cloud shadow map resolution. The resolution is clamped by `r.VolumetricCloud.ShadowMap.MaxResolution`.
Cloud Shadow Ray Sample Count Scale	Scales the number of samples used for shadow map tracing. The sample count resolution is clamped with `r.VolumetricCloud.ShadowMap.RaySampleMaxCount`.

Ray Tracing

These settings apply when the light casts ray traced shadows.

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.
Shadow Source Angle Factor	Scales the source angle used for shadows, relative to Source Angle. The default of 1.0 matches Source Angle.