V-Ray Tip: Real‑World Scene Scale for Accurate V-Ray Lighting

Accurate lighting starts with correct scene scale. If your model isn’t built to real-world size, no amount of tweaking lights or exposure will feel right.

Why scale matters

• Photometric lights (lumens, candelas, nits) and V-Ray Sun & Sky expect real dimensions; 10× too small blows out, 10× too big looks underexposed.
• Depth of Field and Motion Blur operate in scene units; wrong scale makes DOF/MoBlur unnaturally shallow or nearly invisible.
• Many settings are length-based: GI Light Cache sample size, VRayDirt radius, SSS radius, displacement amount, volumetric distances/step size, aerial perspective visibility range, and shadow/secondary-ray bias.

Setup checklist (before lighting)

• Pick system units and stick to them across DCCs. Common pipelines: 1 unit = 1 cm or 1 unit = 1 m (be consistent).
• Sanity-check key dimensions: door ≈ 2 m, chair seat ≈ 0.45 m, car ≈ 4.5 m. If these are off, fix scale first.
• Use physical exposure (V-Ray Physical Camera or Camera Imager in the VFB). For daylight tests: ISO 100, f/8, 1/125 s gets you in the ballpark with Sun & Sky.
• Use photometric light units where possible (lm, cd, cd/m²). Set intensities by real-world references rather than arbitrary multipliers.
• Apply real-world texture scale. Prefer “Use real-world size”/UV tiling by meters or utilize VRayTriplanar/VRayUVWRandomizer with measured values.

Quick diagnostics

• 1 m gray card: Place a 1×1×1 m cube with 0.18 albedo, Sun & Sky at noon. If exposure sits wildly off in the VFB Histogram, check scale or camera settings.
• AO radius probe: VRayDirt at 0.2 m should hug edges, not fill whole rooms. If it floods, the scene is likely oversized.
• DOF spot check: 50 mm, f/8, focus 3 m. If a 100 m space is all sharp, scale’s too big; if everything blurs instantly, it’s too small.

If your scene is already the wrong size

• Rescale with native tools (e.g., 3ds Max Rescale World Units; Maya change Working Units and group-scale; SketchUp Tape Measure scale), then revisit length-based parameters.
• Recompute caches after rescale. Light Cache sample size is in world units—set it proportional to the environment (small value for interiors, larger for exteriors).

Scale-sensitive settings to revisit

• VRayDisplacement amount and any world-unit edge/length controls.
• VRayDirt radius and occlusion distribution.
• SSS (e.g., VRayFastSSS2) radius/scale to match actual material thickness.
• Environment Fog/Aerial Perspective visibility ranges and step size.
• Shadow bias/secondary-ray bias—keep small relative to object size to avoid light leaks or shadow acne.
• Motion Blur shutter vs. object velocities (world units per frame/second).

Pro tips

• Keep a unit-calibrated “reference kit” (meter stick, gray card, standard furniture) in every new scene.
• When using HDRIs, adjust exposure in the Camera Imager rather than arbitrarily scaling dome intensity; verify with the VFB Histogram and false-color.
• Adopt studio templates with locked units and tested defaults. Document them for your team.

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