Lights

A believable lit scene is a fixed three-part rig decided once at startup: image-based fill (an HDR on scene.environment, the dominant fill source) plus one "sun" — a directional light, here a CSM cascaded shadow map, that gives surfaces their shape and casts the shadows — plus a little ambient. The balance principle: all fill (the IBL first, then ambient) must be turned down clearly below the sun, or the shadowed side of every surface floods and cast shadows wash out. The sections below cover the available light combinations, the recipe (IBL fill + one sun + low ambient), the sun with shadows (CSM), the environment and the visible sky, balancing fill vs sun so shadows read, an intensity reference, and why you keep the light set fixed at runtime.

Light combinations

The common rigs and what each produces:

Ambient light controls how shadows appear — without it, shadows are pure black. Even in nighttime scenes, keep enough light (for example an AmbientLight) that the viewer can still see the environment.

The recipe: IBL fill + one sun + low ambient