Materials & lighting: Megalights era

2:00 · Brief Surfaces tell the truth, light tells the time

A material isn't a color — it's a claim about physics. PBR (physically based rendering) means the renderer treats your surface parameters as measurements: how rough, how metallic, how the microsurface scatters light. Get the physics honest and the same material works at noon and midnight. Paint the lighting into the texture, and it works exactly once.

The PBR inputs that do the work

• Base color — the surface's actual albedo, with no lighting or shadows baked in. Real-world albedos are duller than beginners expect.
• Roughness — the single most expressive channel. Variation in roughness (fingerprints, wear, damp) is what makes a surface feel touched.
• Metallic — nearly binary: a thing is a metal or it isn't. In-between values are almost always a mistake.
• Normal — surface detail without geometry. Your scanned Fab assets carry excellent ones; your job is not to fight them.

UE 5.8's Substrate is the engine's newer material authoring model — built for layered, physically complex surfaces like car paint or frosted glass. We'll touch it where it helps, but the master-material-plus-instances discipline below is the workhorse either way: one parent graph, many instances, parameters instead of copies.

Choosing your light engine

• Megalights — production-ready in 5.8: hundreds of dynamic, shadow-casting lights in a scene that would have collapsed under a dozen two years ago. The tool for practical-lit interiors — every lamp, sconce, and screen actually lit.
• Lumen — full dynamic global illumination and reflections; light bounces, color bleeds, the sun moves. The default for rich interiors on desktop.
• Lumen Lite — new in 5.8, targeting 60 fps GI on lighter hardware. It matters to us because Project 3 ships to standalone headsets, where every millisecond is rationed.

The honest answer to "which one" is always the same: the one whose cost you've measured in your scene. Which is this week's discussion.

2:45 · Guided lab Dress and light the blockout

You work on your own Project 1 blockout today. By 4:00 it should have honest surfaces and one deliberate lighting scenario — built by hand, so you can judge what the agent proposes afterward.

1. Build one master material

   In your project's Content/Materials folder, create a material M_Master_Surface. In the material editor, wire texture parameters for base color and normal, and scalar parameters for roughness and a color tint. Parameters — not constants — are the whole point.

2. Derive instances

   Right-click the master → Create Material Instance. Make MI_ instances for your room's three or four dominant surfaces — floor, walls, one accent — using textures from your Fab assets or Fab's surface library. Tune each instance in its editor; note that nothing recompiles.

3. Apply and judge at eye height

   Assign the instances to your blockout geometry, then judge them in PIE at eye height, not from the editor's god view. Tiling scale reads completely differently at 170 cm.

4. Base light rig

   Give the level its world lighting if it lacks it: Directional Light, Sky Atmosphere, Skylight, and Exponential Height Fog (all from the Place Actors panel or the level's environment setup). Rotate the directional light and watch Lumen carry bounce light into the room in real time.

5. Turn on Megalights and go practical

   Enable Megalights for the project (in Project Settings under Rendering, or per-scene as the release notes direct — check the docs open on the projector). Then light the room the way the real one is lit: a fixture per real fixture, at plausible intensities and color temperatures. Add more than you think you're allowed to. That's the era change.

6. Measure, don't vibe

   Console: stat unit and stat gpu. Record your frame time with Megalights on, then disable your practical lights and record it again. This is the verification the State of the Art discussion asked for — vendor claim, meet local evidence.

7. Commit the lit scene

   git commit -am "Week 4: materials + first lighting scenario", push, and screenshot your favorite view for the crit.

4:00 · AI lab Prompt-driven look development

Lighting is where agents look most impressive and deserve the least trust — a render can be pretty and wrong. Today the agent proposes three lighting scenarios for your blockout; you art-direct the best one by hand, like a director working with a fast gaffer.

5:15 · Crit / share One view, one hour

Everyone shows a single view of their room in the chosen lighting scenario and names the hour of day it claims to be. The room votes on whether it's telling the truth. Two weeks to Project 1 crit — from here on, everything is refinement.

Homework — due before Week 5

Resources

• UE 5.8 release notes — the Megalights and Lumen Lite sections are this week's primary reading.
• Epic Developer Community — Learning — the materials and lighting guided courses; both feed the Week 7 exam.
• Claude Code documentation — worth revisiting now that your prompts are getting art-directional.