Definition Lightmap

A lightmap is a pre-rendered texture in which the static light, shadows and indirect lighting of a 3D model or scene are stored. Instead of calculating the light in real time, it is "baked" once and then placed on the model as a texture - ideal for web viewers, AR apps or configurators where performance counts.

How does light mapping work?

Comparison: Lightmap vs. real-time lighting

Compact workflow (5 steps)

1. create a clean UV2 (separate Lightmap UV set)

Create a second UV set just for the lightmap - without overlaps, 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, activate GI/indirect light and make test bakes in low resolution (e.g. 512 px). This way you can see early on whether shadows are too hard or whether leaks occur.

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

3. beacons of the lightmap (if necessary incl. AO)

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 - especially if you want to test different looks.

→ Technical context: Texture Baking (Map Baking)

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

4. integration in viewer/engine

Assign the lightmap correctly in your engine (e.g. lightmap slot in Three.js, Unity or Unreal). Make sure that AO/shadow effects do not run twice (baked AO + SSAO = often too dark).

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

→ Technical deep dive: Unreal Engine & virtual production

5. QA & fine-tuning

Check the target environment for light leaks, moiré, shadows that are too hard or flat artifacts. If necessary, adjust texel density, padding or the light setup. Document the final map settings for later variants.

→ Example of final quality control in a project: Virtual bathroom design - Canyon House

Quick tips

Common mistakes & how to avoid them

• Overlapping UVs: Result: shadow artifacts. Solution: separate UV set for lightmap, no overlaps.
• Too little padding: Color/shadow lines on edges. Solution: Set the edge padding generously.
• Resolution too low: Blurry shadows, loss of detail. Solution: Plan texel density in advance.
• Light leaks: Light "seeps" through thin geometries. Solution: Increase mesh thickness or adjust 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 if I use ray tracing?

Not mandatory. Ray tracing calculates light physically correctly. Lightmaps are still useful to save performance or to load static scenes in web viewers more quickly. More on this under 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?

Depends on the scene. For small product viewers, 512-1024 px is often sufficient. Large rooms / showrooms need 2k-4k, possibly tileable or divided into sectors.

Can I edit lightmaps afterwards?

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 with pre-rendered light and shadow (Lightmap - Wikipedia). It is placed on 3D objects so that lighting does not have to be calculated in real time - ideal for static scenes and performance-sensitive applications.

What light mapping methods does Unity offer - and what are the differences?

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

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

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.