🏠 Interior Lighting

Interior Lighting Principles

Before diving into specific light types, let's establish some fundamental principles that guide all interior lighting work. These concepts come from real-world lighting design and cinematography, and they'll help you make better decisions throughout this lesson.

The Three-Point Lighting Concept

While originally from film and photography, the three-point lighting concept provides a useful framework for thinking about interior spaces:

Key Light: The main, brightest light source that establishes the primary direction of illumination. In interiors, this might be a window, a prominent ceiling fixture, or a focused lamp.

Fill Light: Secondary lighting that softens shadows created by the key light. Ambient bounce from walls, secondary fixtures, or indirect lighting serve this role.

Accent/Rim Light: Lights that highlight specific objects or create separation. Track lighting on artwork, under-cabinet lights, or backlit features.

Figure: Three-point lighting concepts applied to an interior space.

Practical vs. Motivated Lighting

Practical Lights: Light sources that are visible in the scene—lamps, ceiling fixtures, candles, screens. These "justify" the lighting and make it feel grounded in reality.

Motivated Lighting: Additional lights placed to enhance the effect of practicals or create specific looks. The viewer accepts them because they seem to come from visible sources, even if the actual game light is positioned differently.

In game environments, you'll often place a decorative lamp mesh (the practical) and then position an actual Point or Spot Light near it (motivated by the practical) to create the illumination effect.

Light Layering Strategy

Professional interior lighting uses layers:

1. Ambient Layer: Base illumination that prevents pure black shadows. Often from indirect lighting, skylights, or very soft fill lights.
2. Primary Layer: Main light sources that define the space—overhead fixtures, windows, prominent lamps.
3. Accent Layer: Focused lights that draw attention—spotlights on art, under-cabinet lighting, decorative fixtures.
4. Effects Layer: Dynamic or atmospheric lighting—flickering candles, TV glow, lightning flashes.

flowchart TB
    subgraph Layers["Interior Light Layers (Bottom to Top)"]
        direction TB
        L1["🌫️ Ambient Layer
Soft base illumination
Prevents black shadows"]
        L2["💡 Primary Layer
Main fixtures & windows
Defines space character"]
        L3["✨ Accent Layer
Spotlights & highlights
Draws attention"]
        L4["⚡ Effects Layer
Dynamic & atmospheric
Adds life"]
    end
    
    L1 --> L2 --> L3 --> L4
    
    style L1 fill:#607d8b,color:#fff
    style L2 fill:#f1c40f,color:#333
    style L3 fill:#e91e63,color:#fff
    style L4 fill:#9c27b0,color:#fff
                

Figure: Building interior lighting in layers from ambient base to dynamic effects.

Color Temperature in Interiors

Real interior spaces often mix light sources with different color temperatures:

Warm (2700K-3000K): Incandescent bulbs, candles, tungsten. Creates cozy, residential feel.

Neutral (3500K-4500K): Halogen, some LEDs. Clean, professional appearance.

Cool (5000K-6500K): Daylight, fluorescent, modern LEDs. Clinical, modern, or industrial.

Mixing temperatures creates visual interest and realism—warm interior lights contrasting with cool daylight from windows is a classic cinematic look.

Point Lights for Room Illumination

Point Lights emit light equally in all directions from a single point—like a bare light bulb. They're the workhorse of interior lighting, perfect for ceiling fixtures, lamps, chandeliers, and any omnidirectional light source.

Placing and Configuring Point Lights

Placement: Place Actors → Lights → Point Light, or right-click → Lights → Point Light.

Position the Point Light at the location of your practical light source—inside a lamp shade, at the center of a ceiling fixture, at candle flame height.

Essential Point Light Settings

Light Section

Intensity: Brightness of the light. For interior lights, values vary widely:

• Candle: 10-50 lumens
• Table lamp: 200-800 lumens
• Ceiling fixture: 800-3000 lumens
• Bright overhead: 3000-10000 lumens

Light Color: Set directly or use Temperature. Warm whites (2700-3000K) for residential, cooler for commercial/industrial.

Attenuation Radius: How far the light reaches. Beyond this radius, the light has zero contribution. Set this based on the logical reach of your light source—a small lamp might have radius of 300-500 units, a bright ceiling light 1000-2000 units.

Source Radius: Simulates the physical size of the light source for soft shadows. Larger values = softer shadow edges. A small bulb might be 5-10 units; a frosted globe fixture 20-50 units.

Figure: Point Light settings control intensity, reach (attenuation), and shadow softness (source radius).

Shadows

Cast Shadows: Enable for lights that should cast shadows. Disable for fill lights or where performance is critical.

Point Light shadows use cubemap shadow maps—the scene is rendered from 6 directions to create omnidirectional shadows. This makes Point Light shadows more expensive than Spot Light shadows.

Point Light Use Cases

Ceiling fixtures: Position at the fixture location. Adjust attenuation to cover the room appropriately. Multiple fixtures in a large room.

Table/Floor lamps: Place inside or just above the lampshade. Smaller attenuation radius. Warm color temperature for residential feel.

Chandeliers: Can use one Point Light for the whole fixture (simple) or multiple for each candle/bulb (detailed). Consider performance vs. visual quality.

Candles/Flames: Very small attenuation radius, warm orange color (1800-2200K), optionally add flicker with Light Functions or Blueprint.

Ambient fill: Large radius, very low intensity, no shadows. Placed to fill shadow areas without creating additional shadow-casting sources.

Practical + Point Light Pattern

The most common interior lighting pattern combines a visual mesh (the practical) with a Point Light:

1. Place your lamp/fixture mesh
2. Add a Point Light at the bulb location
3. If the fixture mesh blocks light, either make the mesh not cast shadows on self, or place the light just outside the fixture's blocking geometry
4. Add an emissive material to the bulb part of the mesh so it appears to glow

Figure: Combine a visible lamp mesh with a Point Light for realistic fixtures.

Spot Lights for Focused Lighting

Spot Lights emit light in a cone shape, making them perfect for directional interior lighting—recessed ceiling lights, track lighting, flashlights, car headlights, stage spotlights, and any fixture that focuses light in a particular direction.

Spot Light Configuration

Placement: Position the Spot Light at the light source and rotate it to aim where you want the light to fall. The light emits along the negative X-axis (forward) of the actor.

Key Settings

Inner Cone Angle: The angle of full-intensity illumination. Everything within this cone receives maximum light.

Outer Cone Angle: The angle where light falls to zero. The area between inner and outer cones has a smooth falloff. Larger difference = softer edge.

Attenuation Radius: Maximum distance the light travels. Same concept as Point Lights.

Source Radius/Length: For soft shadows. Source Length turns the point into a line (like a fluorescent tube).

Figure: Spot Light cones define full-intensity zone (inner) and falloff zone (outer).

Spot Light Use Cases

Recessed ceiling lights (can lights): Point downward from ceiling. Inner cone 20-40°, outer cone 30-50°. Creates focused pools of light on surfaces below.

Track lighting: Aimed at artwork, displays, or walls. Narrow cones (15-30°) for focused accent, wider for wall washing.

Desk/Task lights: Angled toward work surface. Provides focused illumination for specific areas.

Architectural lighting: Uplights (pointing up walls), downlights (ceiling pointing down), wall washers (angled to graze wall surfaces).

Dramatic effect: Single harsh spotlight creates theatrical, noir, or horror atmospheres.

Spot Lights vs. Point Lights for Performance

When you only need light in one direction, Spot Lights are more efficient than Point Lights:

Figure: Spot Lights need only one shadow map; Point Lights need six.

Spot Light IES Preview

Spot Lights work especially well with IES profiles (covered in detail soon). The cone angles provide a baseline shape, and the IES profile adds realistic distribution patterns on top.

Rect Lights for Area Lighting

Rect Lights (Rectangle Lights) emit light from a rectangular surface rather than a point. This creates the most physically accurate representation of real-world light sources like windows, TV screens, fluorescent panels, and softbox lighting.

Why Rect Lights Matter

Real light sources have physical size. A window isn't a point—it's a large rectangular opening. This size affects how shadows look:

Point/Spot Lights: Create sharp shadows because light comes from a single point (or appears to).

Rect Lights: Create soft shadows with penumbra (partially shadowed edges) because light comes from many points across the surface.

The larger the Rect Light relative to the objects it illuminates, the softer the shadows become. This matches real-world physics.

Figure: Rect Lights create physically accurate soft shadows due to their area nature.

Rect Light Configuration

Placement: Place and orient the Rect Light to match your light source. For a window, align the rectangle with the window opening facing inward.

Key Settings

Source Width / Source Height: The dimensions of the emitting rectangle. Match these to your actual light source size (window dimensions, screen size, panel size).

Barn Door Angle/Length: Optional settings to add "barn door" falloff at the edges, limiting light spread (like theatrical lighting).

Attenuation Radius: How far the light reaches. For windows, this should cover the interior space affected by the window.

Intensity: Typically higher than point lights because you're simulating larger sources. A bright window might need 50,000+ lumens depending on your scene's exposure.

Rect Light Use Cases

Windows: The primary use case. Place Rect Lights at window positions facing into the room. Size matches window dimensions. Creates realistic soft shadows from daylight.

TV/Monitor screens: Emitting colored light into a dark room. The screen's glow on nearby surfaces and characters.

Fluorescent panels: Ceiling-mounted rectangular fixtures common in offices, hospitals, commercial spaces.

Lightboxes/Signs: Illuminated displays, backlit signage, photography softboxes.

Practical large sources: Any rectangular light-emitting surface—illuminated wall panels, ceiling skylights, etc.

Window Lighting Setup

Windows are the most common Rect Light application. Here's a typical setup:

1. Measure your window dimensions in Unreal units
2. Place a Rect Light just inside the window opening, facing into the room
3. Set Source Width/Height to match window size
4. Color: Match your exterior sky (blue-white for daylight)
5. Intensity: Start high (10,000-100,000 lux) and adjust based on auto-exposure
6. Attenuation: Should cover the room depth affected by the window

For best results, combine the Rect Light with a Directional Light (sun) that can cast directional shadows through the window.

flowchart TD
    A["Interior Light Needed"] --> B{"Light Direction?"}
    
    B -->|"All directions"| C["Point Light"]
    B -->|"Focused cone"| D["Spot Light"]
    B -->|"Large area source"| E["Rect Light"]
    
    C --> C1["Lamps, bulbs,
chandeliers, candles"]
    D --> D1["Recessed lights,
track lights, flashlights"]
    E --> E1["Windows, screens,
panels, skylights"]
    
    C1 --> F{"Need soft shadows?"}
    D1 --> F
    E1 --> G["Already soft!"]
    
    F -->|Yes| H["Increase Source Radius"]
    F -->|No| I["Keep Source Radius small"]
    
    style C fill:#f1c40f,color:#333
    style D fill:#e91e63,color:#fff
    style E fill:#2196F3,color:#fff
                

Figure: Choose light type based on the real-world source you're simulating.

Hands-On: Lighting a Complete Interior Room

Now let's bring everything together by lighting a complete interior space. We'll work through a living room scenario, applying the layered lighting approach with multiple light types, IES profiles, and dynamic effects.

Step 1: Set Up Your Room

Start with a basic room structure. You can use BSP brushes, a Starter Content room, or any interior mesh:

1. Create or open a level with an enclosed room (walls, floor, ceiling)
2. Add a window opening on one wall
3. Place basic furniture: couch, coffee table, side table, bookshelf
4. Add a fireplace area (can be simple geometry)
5. Place a picture or artwork on one wall

Don't worry about perfect decoration—focus on having surfaces to receive light and objects to cast shadows.

Figure: Example room layout showing furniture placement and planned light source locations.

Step 2: Establish Ambient Layer (Start Dark)

Begin with everything dark to build up light intentionally:

1. Remove or disable any default Directional Light and Sky Light in your level
2. Your room should now be completely black
3. Add a Sky Light with very low intensity (0.1-0.3) to provide minimal ambient fill
4. Set Sky Light to Stationary or Movable

This ambient layer prevents pure black shadows while keeping the room dark enough to see our lights' contributions clearly.

Step 3: Add Window Light (Primary Layer - Daylight)

The window will be our key light, providing the strongest illumination:

1. Place a Rect Light at the window opening, facing into the room
2. Set Source Width and Source Height to match window dimensions
3. Set Light Color to cool daylight (Temperature: 6000-6500K, or light blue-white)
4. Set Intensity high: start around 20,000-50,000 lumens
5. Set Attenuation Radius to cover the room depth (1500-3000 units)
6. Enable Cast Shadows
7. Set Mobility to Stationary for good quality with reasonable performance

Adjust intensity until the window-side of the room is well-lit with soft shadows. The couch and table should have clear, soft-edged shadows from the window light.

Step 4: Add Ceiling Fixture (Primary Layer - Artificial)

Add a practical ceiling light to fill the center of the room:

1. Place a ceiling light mesh (or simple sphere) in the center of the room
2. Add a Point Light at the fixture location
3. Set Light Color to warm (Temperature: 2700-3000K)
4. Set Intensity moderate: 1500-3000 lumens
5. Set Attenuation Radius to cover most of the room (1000-1500 units)
6. Set Source Radius to 10-20 for slightly soft shadows
7. Consider disabling shadows for this fill light, or keep them subtle

If you have an IES profile for a ceiling fixture, apply it now for more realistic distribution.

Step 5: Add Table Lamp (Primary/Accent Layer)

The table lamp adds warmth and creates a focal point:

1. Place a lamp mesh on the side table
2. Add a Point Light inside or just above the lampshade
3. Set Light Color warm (Temperature: 2700K—incandescent feel)
4. Set Intensity lower: 400-800 lumens (table lamps aren't super bright)
5. Set Attenuation Radius small: 400-600 units
6. Set Source Radius to 15-25 for soft shadows
7. Disable shadows or keep them soft—this is accent lighting
8. Add an emissive material to the lamp's bulb so it glows

The lamp should create a warm pool of light on the table and nearby surfaces, contrasting with the cooler window light.

Step 6: Add Accent Light on Artwork (Accent Layer)

Draw attention to the artwork with a focused spot:

1. Place a Spot Light above and in front of the artwork, angled down at it
2. Set Inner Cone Angle to 15-20°
3. Set Outer Cone Angle to 25-35°
4. Set Light Color neutral (3500-4000K) or slightly warm
5. Set Intensity to make the art clearly visible: 2000-5000 lumens
6. Disable shadows—this is purely for highlighting
7. Optionally apply a track light IES profile

The spotlight should make the artwork "pop" without harsh shadows on the wall.

Step 7: Add Fireplace Glow (Effects Layer)

Create a dynamic, flickering fireplace effect:

1. Place a Point Light at the fireplace opening
2. Set Light Color to warm orange (Temperature: 1800-2200K, or manually set orange)
3. Set Intensity moderate: 1000-2500 lumens
4. Set Attenuation Radius to 500-800 units
5. Set Mobility to Movable (required for Light Functions)
6. Create a Light Function material for flickering (Time → Noise → Lerp 0.5-1.0)
7. Apply the Light Function to the fireplace light
8. Optionally add a second, dimmer Point Light with slightly different flicker timing for complexity

The fireplace should cast dancing, warm light on the nearby floor and furniture, creating a cozy atmosphere.

Figure: All lighting layers working together to create a rich, atmospheric interior.

Step 8: Fine-Tune and Balance

With all lights in place, adjust for balance:

1. Check exposure: Use Post Process Volume auto-exposure or manually adjust to ensure nothing is blown out or too dark
2. Balance temperatures: Verify the warm/cool contrast between window (cool) and interior lights (warm) reads well
3. Shadow quality: Ensure key shadows (from window) are sharp enough to read while fill lights don't create confusing secondary shadows
4. Disable unnecessary shadows: Fill lights and accent lights usually don't need shadows
5. Check from multiple angles: Walk through the room in Play mode to verify lighting works from different viewpoints

Step 9: Build Lighting (If Using Static/Stationary)

If you're using Static or Stationary lights:

1. Go to Build → Build Lighting Only
2. Start with Preview quality for fast iteration
3. Once satisfied, build at Production quality for final results
4. Review the lighting build log for any errors or warnings

Final Checklist

flowchart LR
    subgraph Ambient["1️⃣ Ambient Layer"]
        A1["Sky Light
Very low intensity"]
    end
    
    subgraph Primary["2️⃣ Primary Layer"]
        P1["Window Rect Light
Cool daylight"]
        P2["Ceiling Point Light
Warm artificial"]
    end
    
    subgraph Accent["3️⃣ Accent Layer"]
        AC1["Table Lamp
Warm pool"]
        AC2["Art Spotlight
Focused highlight"]
    end
    
    subgraph Effects["4️⃣ Effects Layer"]
        E1["Fireplace
Flickering warmth"]
    end
    
    Ambient --> Primary --> Accent --> Effects
    
    style Ambient fill:#455A64,color:#fff
    style Primary fill:#1976D2,color:#fff
    style Accent fill:#7B1FA2,color:#fff
    style Effects fill:#E65100,color:#fff
                

Figure: Complete interior lighting follows the four-layer approach from ambient base to dynamic effects.

Summary

In this lesson, you've learned to light interior spaces using Unreal Engine 5's lighting tools. Interior lighting requires a thoughtful, layered approach that combines multiple light types to create realistic, atmospheric environments.

Key Concepts

Interior Lighting Principles: Adapt three-point lighting for interiors using key, fill, and accent lights. Use practical lights (visible fixtures) with motivated lighting (actual light sources). Build lighting in layers: Ambient → Primary → Accent → Effects.

Point Lights: Emit light in all directions from a single point. Perfect for ceiling fixtures, table lamps, chandeliers, and candles. Control intensity, attenuation radius, source radius, and color temperature. Shadows use expensive cubemap rendering—disable on fill lights.

Spot Lights: Emit light in a cone shape. Ideal for recessed ceiling lights, track lighting, flashlights, and dramatic accents. Configure inner/outer cone angles for edge softness. More efficient shadows than Point Lights (single shadow map vs. six).

Rect Lights: Emit from a rectangular surface, creating physically accurate soft shadows. Essential for windows, TV screens, and fluorescent panels. Larger source = softer shadows. Most expensive for shadow computation—use strategically.

IES Profiles: Industry-standard files defining real fixture light distribution. Import .ies files and apply to Point/Spot Lights for photometrically accurate patterns. Minimal performance cost for significant realism improvement.

Light Functions: Material-based light modifiers for dynamic effects. Create flickering, pulsing, projected patterns, and color variations. Requires Movable mobility. Use Time + Noise nodes for organic animation.

Best Practices

• Start dark, add light: Build up lighting intentionally rather than fighting "light soup"
• Mix color temperatures: Warm interiors + cool daylight creates cinematic contrast
• Disable shadows selectively: Only key lights need shadows; fill and accent usually don't
• Use practical + light combos: Place visible fixtures with actual light sources nearby
• Match IES to fixture type: Use appropriate profiles for each fixture style
• Consider performance: Rect > Point for shadow cost; Light Functions add shader overhead

Figure: The five key tools for interior lighting in Unreal Engine 5.

Knowledge Check