Reflection Probe
Pre-captured cubemap for local reflections
Also known as: Reflection capture · Cubemap probe
Definition
A reflection probe captures a cubemap snapshot of the environment at a specific point in a level, used to drive reflections on nearby surfaces. Before ray-traced or screen-space reflections, probes were the only way to give real-time materials accurate reflections of their surroundings — and even now they remain the cheap fallback for off-screen reflections. UE5 Lumen still uses probe data for distant indirect reflections.
In production
Place probes strategically in level: one per interior room, one per outdoor zone, one near each large reflective surface (puddles, polished floors). Too many probes increase build time and memory; too few produce mismatched reflections at zone boundaries, visible as a sudden pop when a character walks from one probe's influence volume into another's. UE5 supports both baked Reflection Captures (Sphere and Box variants) for static lighting scenarios and Lumen's real-time reflections for fully dynamic scenes, with probes still used as a distance fallback since Lumen's screen-space and ray-traced reflections only cover what's actually on screen. A common mistake is placing a single probe at room centre in a large or irregularly shaped room, which produces inaccurate reflections near the walls — box-projected probes correct for this by remapping the cubemap to the room's actual bounding geometry.
