V-Ray Tip: Portal Lights and ADL: Optimize Daylight Interior Sampling

For daylight interiors lit through windows or doors, portal lights guide V-Ray’s sampling toward the bright openings, reducing GI noise and cutting render times—especially with HDRI-driven sky lighting.

• What portal lights do: They don’t add light; they focus environment sampling where light actually enters, improving efficiency and stabilizing indirect bounces.
• Best for: Rooms with small/medium apertures, deep interiors, and HDRIs with strong contrast.

Modern V-Ray guidance:

• V-Ray Next and newer: Prefer the Adaptive Dome Light (ADL). It automatically performs “portal-like” optimization—no manual portals required in most cases.
• When to still use portals: Legacy projects without ADL; specific host limitations; or edge cases with extreme occlusion where manual control yields cleaner noise.

Manual portal workflow (when applicable):

• 3ds Max: Use VRayLight set to Plane, enable Skylight portal. Choose Simple for speed or Accurate if you need the HDRI’s color variation indoors. Set Invisible so it doesn’t appear in reflections.
• Maya: Use VRayRectLight, enable Portal light (Simple/Accurate modes). Place it flush with the window, normal facing inward.
• Rhino/SketchUp: Rely on the Dome Light with Adaptive enabled (no manual portals); refine Dome subdivisions or use Light Mix to balance.

Placement and setup tips:

• Cover the opening tightly; avoid oversized or overlapping portals.
• Keep them coplanar with the aperture and as close as possible to glazing/frames.
• Normals must face the interior; disable double-sided unless the opening is double-sided by design.
• Use Simple mode to reduce noise quickly; switch to Accurate only if color fidelity from the HDRI is essential.

Performance and quality notes:

• Pair with Brute Force + Light Cache for robust GI; raise Light Cache samples modestly on large interiors.
• Denoise after convergence; the VFB Denoiser cleans residual speckle without masking lighting errors.
• Clamp bright outliers (Max Ray Intensity or RGB Clamp) to tame fireflies from glossy/glass edges near openings.

Troubleshooting quick checks:

• If noise persists, verify scale, camera exposure, and that portals precisely match openings.
• Test ADL only versus manual portals using Region Render and VFB History; keep the faster, cleaner option.
• Reduce glossy/refraction depth for background fixtures to lower secondary noise overhead.

Adopt the simplest setup that delivers clean interiors fast—today, that often means the Adaptive Dome Light alone. For legacy scenes or niche cases, well-placed portals remain a powerful optimization.

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