V-Ray Tip: Physically Based V-Ray Sun-to-Sky Balance

Balancing V-Ray Sun and Skylight ensures natural contrast, believable color, and readable interiors/exteriors without heavy post. Start physically correct, then nudge the ratio with scene-aware controls.

Establish a physically plausible baseline

• Create a V-Ray Sun and link a VRaySky to the environment GI slot. Keep both multipliers at 1.0 for a neutral starting point.
• Use the Improved/PRG or Hosek sky model for more accurate horizon and zenith color. Preetham can look clean but less nuanced.
• Scene scale matters: use real-world units; wrong scale skews light behavior and exposure.

Dial the sun-to-sky ratio (without breaking physics)

• Prefer adjusting turbidity over brute-force multipliers:
  • Turbidity 2.0–3.0: crisp, blue skies; higher sun contrast.
  • Turbidity 4.0–6.0: hazier, brighter dome; softer sun vs sky balance.
• Ozone 0.2–0.4 keeps sky hue believable; higher values push toward cyan, which can overpower interiors.
• For interiors with window light, aim for a sun:sky ratio of roughly 2:1 to 4:1. If windows blow out, lower sun slightly (0.7–0.9) or increase turbidity a touch rather than cranking camera exposure.
• Keep GI, reflection, and refraction environment multipliers aligned (around 1.0) unless you have a specific look-dev reason to separate them.

Camera exposure: match photography

• Daylight exteriors: target EV ≈ 14–15 (for ISO 100). Interiors lit by windows: EV ≈ 11–13. Use ISO/Aperture/Shutter instead of arbitrary light multipliers.
• White Balance “Daylight” (≈ 6500K) provides a neutral baseline; adjust to taste only after the light ratio feels right.
• Use the VFB Exposure/Highlight Burn for headroom; avoid globally clamping too early or you’ll lose dynamic range needed to judge balance.

Iterate fast with LightMix

• Add Light Select/LightMix for Sun and Sky groups. Render once, then re-balance in the VFB non-destructively.
• When you like the ratio, “To Scene” to bake gains back into lights for consistent animation renders.

Common pitfalls and fixes

• Double environment: Don’t place VRaySky in both host environment and V-Ray Environment GI simultaneously unless intended.
• Oversoft sun: Increasing Sun size softens shadows but doesn’t significantly change overall illuminance; compensate visually, not with extreme multipliers.
• Flat interiors: If the sky overwhelms the sun, lower turbidity or slightly raise the sun (1.1–1.3) and verify exposure before adding fill lights.

Quick recipe to try

• Sun Multiplier 1.0; Size 3.0 (soft but defined shadows)
• Sky Model: Improved/PRG; Turbidity 2.5; Ozone 0.35; Ground Albedo 0.2
• Camera: ISO 100, f/8, 1/200s (≈ EV 15), WB Daylight
• Fine-tune ratio in LightMix, then bake “To Scene.”

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