V-Ray Tip: V-Ray Light Portals — Placement and Best Practices

Light portals can significantly improve interior daylight renders—when used in the right scenarios. Here’s how to decide, place, and tune them for clean, fast results.

When to use light portals

• Using Adaptive Dome Light (default in modern V-Ray): Skip portals. The Adaptive Dome already importance-samples windows and skylight more efficiently; portals can slow you down.
• Older scenes or legacy workflows without Adaptive Dome Light: Use portals to guide sampling through windows/doors when the environment lighting is the primary source.
• Artificial-light-only interiors: Do not use portals; they provide no benefit.

How to set up portals (legacy/when needed)

• Use a VRayLight Rectangle sized to each exterior opening (window, skylight, door). Place it snugly in the opening, facing into the room.
• Enable the Portal/Skylight Portal mode on the light. In most hosts, intensity and color are ignored because the environment drives the light.
• Set the light to Invisible so it doesn’t appear or cast direct highlights. Avoid Double-Sided; you want the portal to “pull” samples inward.
• For irregular openings, use a few non-overlapping rectangles instead of one oversized portal that covers walls—oversized portals waste samples and add noise.

Glass and exposure considerations

• Place portals on the room side of the glazing to avoid sampling through multiple glass layers.
• For thin window glass using VRayMtl, consider enabling Affect Shadows to prevent overly dark GI contributions behind the glass.
• Use a physical camera workflow (ISO, shutter, f-number) and lock exposure before you compare portal vs. non-portal tests.

Sampling and GI settings that pair well

• Brute Force + Light Cache is a solid baseline for interiors. Portals help BF sample the environment more efficiently in legacy setups.
• Keep your Noise Threshold consistent (e.g., 0.01–0.03 for lookdev, 0.005–0.01 for finals) when A/B testing.
• Use Adaptive Lights and keep light counts manageable—portals don’t replace good light hygiene.

Diagnose and validate

• Check the Noise Level and Sample Rate render elements; portals should reduce noise bands around openings in non-ADL workflows.
• Use VFB History to compare with/without portals at identical settings. Keep only what measurably improves time-to-clean.

Modern best practice

• Prefer a Dome Light with Adaptive Dome enabled for HDRI/sky interiors—no portals needed, on both CPU and GPU.
• If converting a legacy scene, first remove/disable portal mode, enable Adaptive Dome, re-tune exposure, and re-evaluate noise threshold.

Quick checklist

• Is Adaptive Dome Light on? If yes, do not use portals.
• If portals are used: one per opening, inward-facing, Invisible on, no overlap.
• Verify glass settings (Affect Shadows) and retune exposure before judging results.

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