V-Ray Tip: Reuse Single Light Cache Prepass for Camera-Only Animation

Speed up global illumination by computing a single Light Cache prepass and reusing it across frames.

What this does

• Computes the secondary GI once (as a prepass), then reuses it for every frame in a camera move.
• Eliminates repeated GI calculations, reducing render times and GI flicker when the camera is the only animated element.

When to use it

• Camera fly-throughs with static geometry, materials, and lights.
• Lookdev turntables or layout reviews where only the camera changes.
• Hybrid workflows: Light Cache as secondary GI + Brute Force (or Irradiance Map) as primary.

Setup workflow (typical)

• Set GI secondary engine to Light Cache.
• Enable Fly-through/Camera Path mode to gather samples along the full animation path. Treat this as your “prepass.”
• Choose a stable sample size in scene units (see guidance below).
• Render the prepass once, save the Light Cache to file.
• Switch Light Cache to From File and point all render nodes to the cache for finals.

Key parameters that matter

• Subdivs: Start at 1500–2000 for 1080p interiors; 2500–4000 for complex scenes or 4K. Increase only if you see splotches in corners or under furniture.
• Sample Size: 0.02–0.03 scene units for interiors; 0.03–0.05 for exteriors. Keep consistent with real-world scale for predictable results.
• Filter/Prefilter: Enable modest prefiltering to reduce minor flicker (use conservative values); avoid over-smoothing which can wash out detail.
• Use Light Cache for Glossy Rays: Off for animation to avoid temporal blurring; consider On for stills if it meaningfully reduces glossy noise.

Performance and quality tips

• Light Cache is resolution-independent; you can compute the prepass at a lower resolution and reuse it at final resolution if sample size is set in world units.
• Avoid “Store direct light” for general work; direct lighting is better handled by the primary GI and lights.
• Lock exposure, color mapping, and camera settings before generating the prepass to keep GI consistent.
• If any objects or lights must move, keep them excluded from the Light Cache reliance (switch those shots to full Brute Force secondary or regenerate the cache per change).
• For render farms, place the LC cache on shared storage and use From File on all nodes to ensure identical GI.

Troubleshooting

• Splotches/blotches: Raise Subdivs moderately or lower Sample Size slightly; check material normals and overlapping faces.
• Shimmering edges: Increase prefiltering a bit or ensure glossy rays are not using LC in animation shots.
• Mismatched frames on the farm: Verify all nodes can access the same LC file path.

Pipeline note

• Archive the Light Cache with the shot package so re-renders later don’t require regeneration.

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