A lightmap is a performance-optimized texture into which highly complex lighting information (direct light, soft shadows, global illumination) is permanently "baked" during pre-production (baked lighting). This significantly reduces the load on the graphics card, since end devices no longer have to perform these complex shadow calculations in real time.

What should be the size of a lightmap?

Memory management (VRAM) is critical: For standalone product viewers, optimized textures ranging from 512 to 1024 px are often sufficient. Complex B2B brand spaces (virtual showrooms) require maps in 2K to 4K resolution. A consistent texel density (pixels per meter) is essential to ensure razor-sharp shadows without compromising performance.

What are lightmap UVs, and why are they critical?

Lightmaps absolutely require a second, dedicated set of UV coordinates (UV2). Unlike material UVs, the so-called UV islands in lightmap UVs must never overlap (No Overlapping). An improper setup leads to severe rendering artifacts, in which an object’s shadow is incorrectly cast onto a completely different component.

How can I prevent errors like "light bleeding"?

Light bleeding (light leaks along edges) is a common error in untested 3D pipelines. Professional 3D studios prevent this by using an accurate UV2 unwrap with sufficient "padding" (pixel spacing between UV islands) and by increasing the lightmap resolution in geometrically complex areas. This ensures flawless visual quality.

Can I edit finished lightmaps after the fact?

Minor adjustments to contrast or brightness (color grading) can be easily made in tools like Photoshop. However, manually retouching the shadow shapes is strongly discouraged. As soon as the rendered shadows no longer physically match the 3D geometry and light source exactly, the photorealistic illusion collapses immediately. In such cases, a clean "re-bake" is always the better choice.

Lightmap explained - definition, workflow, advantages & tips

Q: Do I need lightmaps when I use ray tracing?

Physical ray tracing is the standard for high-end offline rendering. However, lightmaps remain indispensable in spatial computing (VR/AR) and for interactive e-commerce configurators (WebGL) on mobile devices. They ensure photorealistic lighting at maximum frame rates (60+ FPS) without the extreme hardware demands of real-time ray tracing.

Glossary

What is a lightmap?

Daniel Schuster

•

Last updated:

September 10, 2026

In this glossary article:

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Glossary

What is a lightmap?

Daniel Schuster

•

Last updated:

September 10, 2026

Definition of Lightmap

A lightmap is a pre-rendered texture that stores the static lighting, shadows, and indirect lighting of a 3D model or scene. Instead of calculating the lighting in real time, it is “baked” once and then applied to the model as a texture—ideal for web viewers, AR apps, or configurators where performance matters.

How does lightmapping work?

Set up the scene with a fixed lighting setup (position, color, intensity).
Create clean UV coordinates for the lightmap without any overlaps (second UV set).
The rendering engine calculates the lighting (direct light, diffuse GI, AO) for each texel.
The result is saved as a texture (lightmap, sometimes combined with AO/shadow maps).
In the viewer or the game engine, the lightmap is multiplied or overlaid—the object appears “illuminated” without any real-time calculations.

Comparison: Lightmap vs. Real-Time Lighting

Criterion	Lightmap (baked)	Real-Time Lighting / Ray Tracing
Performance	Very high – minimal computational overhead at runtime	Depends on hardware; often expensive
After the lighting changes	Low – needs to be baked again	High – Changes are visible immediately
Texture / Appearance	Very consistent, no noise or flicker	May vary (noise, sampling artifacts)
Production Costs	Additional Setup (UV2, Bake Settings)	Less setup, but higher rendering costs

3D rendering of a bright living room with a brown leather sofa and a view of the surrounding nature through large windows

From Technical Term to Visual Experience

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Streamlined Workflow (5 Steps)

1. Set up UV2 correctly (separate lightmap UV set)

Create a second UV set specifically for the lightmap— without overlaps and with sufficient padding (at least 4–16 px). This prevents color bleeding and shadow artifacts later on.

→ More on clean UV/map preparation: Preparing digital surfaces & textures

2. light setup & test bakes

Define key, fill, and rim lights, enable GI/indirect lighting, and create test bakes at a low resolution (e.g., 512 px). This way, you can see early on if shadows are too harsh or if there are any leaks.

→ Take a look at how we use light specifically for animations: 3D animation & video

3. Lightmap beacons (including AO, if applicable)

Bake the lightmap (optionally combined with AO) in 16-bit, linear. Don't forget edge padding. Keeping AO separate can give you more flexibility later on—especially if you want to test different looks.

→ Technical Context: Texture Baking (Map Baking)

→ Example of baked shadows for cut-outs: Cut-outs & packshot renderings

4. Integration into the Viewer/Engine

Assign the lightmap correctly in your engine (e.g., lightmap slot in Three.js, Unity, or Unreal). Make sure that AO and shadow effects aren't running simultaneously (baked AO + SSAO often results in the image being too dark).

→ Real-time/VR context: 360° tour & virtual reality

→ Technical deep dive: Unreal Engine & virtual production

5. QA & fine-tuning

In the target environment, check for light leaks, moiré, shadows that are too harsh, or area-wide artifacts. If necessary, adjust the texel density, padding, or lighting setup. Document the final map settings for future variations.

→ Example of final quality control in a project: Virtual Bathroom Design – Canyon House

Quick Tips

UV padding: At least 4–16 pixels (depending on resolution) to prevent bleeding.
Plan the resolution: Don't make the lightmap too large (mobile!), but make it large enough so that details don't get washed out.
Combining: AO can be applied separately or baked into the lightmap—watch out for “dirty edges.”
Linear vs. sRGB: Bake in the linear color space, then select the correct color profile later.
Fallbacks: For assets with changing materials, it's better to keep the AO separate and use the lightmap only for indirect lighting.

Common mistakes & how to avoid them

Overlapping UVs: Result: shadow artifacts. Solution: Create a separate UV set for the lightmap; avoid overlaps.
Insufficient padding: Color/shadow fringes along the edges. Solution: Set the edge padding to a generous value.
Resolution too low: Blurry shadows, loss of detail. Solution: Plan the texel density in advance.
Light Leaks: Light “seeps” through thin geometries. Solution: Increase the mesh thickness or adjust the lightmap cage.
AO & Lightmap double: AO baked AND SSAO active → corners too dark. Solution: use only one variant or adjust values.

FAQ – Lightmaps

Do I need lightmaps when I use ray tracing?

Not necessarily. Ray tracing calculates lighting in a physically accurate way. Lightmaps are still useful, however, for improving performance or loading static scenes faster in web viewers. For more information, see Ray Tracing.

Which maps complement lightmaps in a PBR workflow?

At least BaseColor, Normal, Roughness/Metalness. Ambient Occlusion (AO) can be baked in or used separately. See Normal Map & Ambient Occlusion (AO).

How big should a lightmap be?

It depends on the situation. For small product viewers, 512–1024 px is often sufficient. Large rooms or showrooms require 2k–4k resolution, possibly tileable or divided into sectors.

Can I edit lightmaps after the fact?

Yes, but carefully. Adjusting brightness/contrast is okay - changing shadow shapes is not. Otherwise the light color & GI are no longer correct. Better to bake again.

What is a lightmap, by definition—and what is it used for?

A lightmap is a texture containing pre-rendered light and shadows (Lightmap – Wikipedia). It is applied to 3D objects to avoid having to calculate lighting in real time—ideal for static scenes and performance-sensitive applications.

What lightmapping techniques does Unity offer—and what are the differences?

Unity provides several lightmappers, such as the Progressive CPU/GPU Lightmapper (Unity Lightmappers). They differ in terms of speed, memory usage, and the quality of indirect lighting.

How do I correctly set the resolution (texel density) of my lightmap?

In many pipelines, a fixed texel density is selected per unit area. Tools such as the Source/Valve engine provide guidelines and workflows - see Lightmap in the Valve Developer Community. Important: plan enough UV area & padding, otherwise shadows will become muddy or fray.