01 — Unit Glossary
| Unit | Symbol | Measures | Real Camera | Octane | Redshift | Unreal 5 | Notes |
|---|---|---|---|---|---|---|---|
| Candela | cd | Luminous intensity in one direction | Fixture datasheets | Sphere/Spot (Power mode) | Physical Light (cd) | Point, Spot lights | UE5 defaults cd for points/spots; RS Physical Light exposes unit selector |
| Lumen | lm | Total luminous flux emitted | Bulb packaging | Area lights (Power) | Physical Light (lm) | Rect / Area lights | Integrates intensity over solid angle |
| Lux | lx | Illuminance at surface (lm/m²) | Light meter reading | — | — | Sky Light / Directional | Falls off with distance² |
| Nit | cd/m² | Luminance — surface brightness | Monitor / display spec | — | Physical Light (nits) | Emissive material intensity | HDR displays: 400–10,000 nits |
| Foot-candle | fc | Illuminance (imperial) lm/ft² | Film/TV on-set standard | — | — | — | 1 fc = 10.764 lux |
| EV (Exposure Value) | EV | Log₂ scale of exposure | Core camera param | Imager exposure | Camera EV / f-stop/shutter/ISO | Post Process EV100 | Each +1 EV = 2× brighter |
| Watt (radiometric) | W | Radiant power, not perceptual | Flash / strobe power | Legacy Power mode | Scene-relative intensity | — | Renderer "watts" ≠ real watts; scene-relative |
| Kelvin (CCT) | K | Color temperature of source | WB dial, gels | Light color temp | Light color temp (K picker) | Light color temp | Universal across all four |
02 — Real-World Intensity Reference
| Light Source | Lux at subject | Foot-candles | Approx EV (ISO 100) | Color Temp |
|---|---|---|---|---|
| Direct midday sun | 100,000 lx | 9,300 fc | 15–16 EV | 5,500–6,500 K |
| Overcast sky | 10,000 lx | 930 fc | 12–13 EV | 6,500–7,500 K |
| Sunrise / Sunset | 1,000–5,000 lx | 93–465 fc | 11–13 EV | 2,000–3,500 K |
| Indoor office (fluorescent) | 300–500 lx | 28–46 fc | 9–10 EV | 4,000–5,000 K |
| Tungsten work light 500W | 1,000–5,000 lx @1m | 93–465 fc | — | 2,800–3,200 K |
| Candlelight | 10–15 lx | ~1 fc | 6–7 EV | 1,800–2,000 K |
| Full moon (clear night) | 0.05–0.1 lx | 0.005 fc | 1–3 EV | 4,100 K |
| Film set HMI 1.2kW @3m | ~3,000 lx | ~279 fc | — | 5,600 K |
03 — Octane Render Light Settings
| Light Type | Power Unit | Typical Range | Distribution | Equiv. Real Source | Notes |
|---|---|---|---|---|---|
| Daylight (Sun) | Intensity (relative) | 1.0 default | Directional | Direct sun | Turbidity 2–6 for weather states |
| Area Light | Power (W) | 10–10,000 W | Lambertian | Softbox / LED panel | Size affects softness; supports texture emission |
| Sphere / Point | Power (W) | 50–5,000 W | Isotropic | Practical bulb | Radius affects shadow softness |
| Spot Light | Power (W) | 100–5,000 W | Cone + falloff | Fresnel / ERS spot | Supports IES photometry profile |
| HDRI Environment | Intensity multiplier | 0.5–4.0 | Full spherical | Real environment | 1.0 = physically calibrated if real-world captured |
| Emissive Material | Texture Emission power | 1–10,000+ W | Surface normal | Neon / screen / LED strip | Bake into mesh for GI contribution |
04 — Octane Camera / Exposure Params
| Parameter | Octane Default | Real Equiv. | Range | Notes |
|---|---|---|---|---|
| F-stop (Aperture) | f/2.8 | f/2.8 | f/0.9–f/32 | Affects DOF + exposure |
| Shutter Speed | 1/250 | 1/250 sec | 1–1/4000 | Affects motion blur + exposure |
| ISO | 100 | ISO 100 | 50–6400+ | ↑ ISO = ↑ noise grain in render |
| Response (tone map) | sRGB linear 1.0 | Film response | Multiple presets | ACES / filmic for cinematic look |
| White Balance | 6500 K | Daylight WB | 1000–12000 K | Match to dominant light source |
| Vignette | 0.0 | Lens falloff | 0–1 | Subtle 0.1–0.3 for cinema feel |
05 — Redshift Light Settings
| RS Light Type | Intensity Unit | Typical Range | Distribution | Equiv. Real Source | Notes |
|---|---|---|---|---|---|
| Physical LightArea / Rect | Selectable: W, lm, cd, nits | 100–10,000 W / 1,000–50,000 lm | Lambertian | Softbox / LED panel | Unit selector in light attributes; physically accurate when set to lm/cd. |
| Dome LightIBL / Sky | Exposure (EV) or multiplier | 0.5–4.0 mult / EV ±3 | Full spherical | HDRI environment | Use Background Plate for separate BG vs. lighting; portal lights boost interior accuracy |
| Directional LightSun | Intensity (relative) | 1.0 default | Parallel rays | Direct sunlight | Combine with RS Sky node or Physical Sky |
| Point / Spot LightOmni / cone | Selectable: W, lm, cd | 800 cd / 50,000 cd (spot) | Isotropic / cone | Practical bulb / stage spot | IES profile supported; Decay Rate: Quadratic = physically correct |
| Portal LightWindow assist | Intensity multiplier | 1.0 (pass-through) | Directional funnel | Window / doorway | Guides dome/sky light inward for faster interior GI convergence |
| Emissive MaterialRS Light Material | Selectable: W, lm, cd, nits | 100–10,000 nits / 500–5,000 W | Surface normal | Neon / screen / LED strip | Enable "Visible in Reflections" and "Affect GI" for full contribution |
| RS Sun & SkyPhysical atmosphere | Intensity + turbidity | 1.0 sun / turbidity 2–8 | Rayleigh + Mie scatter | Outdoor atmosphere | Turbidity 2 = very clear; 8 = heavy haze |
06 — Redshift Camera / Exposure Params
| Parameter | RS Default | Real Equiv. | Range | Notes |
|---|---|---|---|---|
| F-stop (Aperture) | f/5.6 | f/5.6 | f/1.0–f/32 | Physical camera tag in C4D/Maya/Houdini; DOF + exposure |
| Shutter Speed | 1/60 sec | 1/60 sec | 1–1/8000 | 180° rule: 1/(fps × 2) |
| ISO | 100 | ISO 100 | 50–6400+ | Raises gain; use Film Grain node to add matching noise |
| Exposure Compensation | 0 EV | Exposure comp dial | –5 to +5 EV | Post-render EV comp; non-destructive override |
| White Balance | 6500 K | Daylight | 1500–12000 K | In RS Camera or Post FX node |
| Tone Mapping | Photographic / ACES | Film response | Linear, Photographic, ACES, Reinhard | ACES recommended for cinematic; Photographic for commercial product |
| Vignette | 0.0 | Lens falloff | 0–1 | In RS Post FX; combine with chromatic aberration for lens feel |
07 — Unreal Engine 5 Light Settings
| UE5 Light Type | Intensity Unit | Typical Value | Real Equiv. | Notes |
|---|---|---|---|---|
| Directional LightSun / Moon | Lux | 100,000 lx (sun) · 0.1 lx (moon) | Direct sunlight | Lumen + Sky Atmosphere for physical sky |
| Sky LightAmbient dome | Lux or EV | 1–50,000 lx | Overcast / HDRI sky | Capture scene or HDRI cubemap; recapture when lights change |
| Point LightPractical / omni | Candela | 800 cd (60W) · 1600 cd (100W) | Practical bulb | Inverse square falloff; adjust Attenuation Radius |
| Spot LightTheatrical / car | Candela | 2,000–50,000 cd | Stage spot / headlight | Inner/Outer cone angles; IES texture supported |
| Rect LightSoftbox / panel | Lumen | 1,000–10,000 lm | LED panel / softbox | Width × Height = area; Barn Door angles; source texture supported |
| Emissive MaterialScreen / neon | cd/m² (nits) | 100–10,000 nits | Monitor / LED strip | Enable "Emissive for GI" for Lumen; scale via Emissive Boost |
| Sky AtmospherePhysical sky | Managed by system | Driven by Directional | Rayleigh / Mie scatter | Aerosol density drives haze; scattering scale for atmosphere thickness |
08 — Unreal Engine 5 Camera / Exposure
| Param | UE5 Default | Real Equiv. | Typical Range | Notes |
|---|---|---|---|---|
| Auto Exposure Method | Manual / Auto Histogram | Exposure meter | Histogram or Luminance | Manual = use EV100; Auto = set Min/Max EV |
| EV100 | 0 | f/1.0 · 1s · ISO 100 | –4 to +20 | Physically calibrated; match to scene lux |
| ISO (Cine Cam) | 100 | ISO 100 | 50–3200 | CineCamera Actor exposes full lens params |
| F-stop (Cine Cam) | f/5.6 | f/5.6 | f/1.4–f/22 | Controls DOF; sensor size determines CoC |
| Shutter Speed (Cine Cam) | 1/24 sec | 180° rule | 1/16–1/8000 | Motion blur follows 180° shutter rule (fps × 2) |
| White Balance | 6500 K | Daylight | 1500–15000 K | Post Process Volume; tint slider for green/magenta offset |
| Tone Mapper | ACES filmic | Film/Grade LUT | Filmic / custom LUT | Apply Resolve LUT for match; Film Slope/Toe/Shoulder adjustable |
09 — Color Temperature Reference
10 — Conversion Formulas
EV ↔ Lux
EV = log₂(Lux / 2.5)
Lux = 2.5 × 2^EV
Lux = 2.5 × 2^EV
Assumes reflected-light metering at ISO 100.
Lumen ↔ Candela
lm = cd × Ω (steradians)
Point: lm = cd × 4π ≈ cd × 12.57
Spot: lm = cd × 2π(1 − cos θ)
Point: lm = cd × 4π ≈ cd × 12.57
Spot: lm = cd × 2π(1 − cos θ)
θ = half-angle of spot cone
Foot-candle ↔ Lux
lx = fc × 10.764
fc = lx ÷ 10.764
fc = lx ÷ 10.764
100 fc ≈ 1,076 lx. US film/TV uses fc; metric DPs use lux.
Inverse Square Law
E₂ = E₁ × (d₁ / d₂)²
Double distance → ¼ lux
Triple distance → 1/9 lux
Double distance → ¼ lux
Triple distance → 1/9 lux
Applies in real, Octane, RS (Quadratic), and UE5.
UE5 EV100
EV100 = log₂(N² / t × 100/S)
EV100 = log₂(Lux / 1.2)
Noon sun 100,000 lx → EV100 ≈ 16.4
EV100 = log₂(Lux / 1.2)
Noon sun 100,000 lx → EV100 ≈ 16.4
Use Manual Exposure in Post Process for physical accuracy.
Octane / RS Power → Lux
No direct formula — relative.
Anchor camera EV to real-world
lux reference, scale lights to match.
Anchor camera EV to real-world
lux reference, scale lights to match.
RS Physical Lights in lm/cd are closer to physical but still require camera calibration.
11 — Quick Reference: Common Scene EV Values
Direct Noon Sun
EV 15–16
100,000 lx · 5500–6500 K
Overcast Day
EV 12–13
10,000 lx · 6500–7500 K
Sunset / Golden Hour
EV 11–13
2,000–3,500 K · warm orange
Interior Daylight Window
EV 10–12
300–2,000 lx indirect
Bright Office Interior
EV 9–10
300–500 lx · 4000 K fluoro
Restaurant / Bar
EV 7–8
50–100 lx · 2800–3200 K
Candlelit Room
EV 6–7
10–15 lx · 1800 K
City Night Street
EV 4–6
5–20 lx · mixed sources
Moonlit Night
EV 1–3
0.05–0.1 lx · 4100 K
Starlight only
EV −6
0.001 lx
12 — Cross-App Workflow Comparison
| Task | Real Camera | Octane | Redshift | Unreal Engine 5 |
|---|---|---|---|---|
| Match exposure to scene | Meter → f-stop / shutter / ISO | Set camera EV, scale light Power | Set camera ISO/f-stop or EV comp; use Physical Lights in lm/cd | Set EV100 in Post Process; match scene lux |
| Practical bulb light | 60W = ~800 lm · 2700 K | Sphere ~200–800W · 2700 K | Point Light 800 cd or 800 lm · 2700 K | Point Light 800 cd · 2700 K |
| Simulate noon sun | f/16 · 1/250 · ISO 100 | Daylight Intensity 1.0 · Turbidity 2 | RS Sun node · Turbidity 2 · Intensity 1.0 | Directional 100,000 lx · Sky Atmosphere on |
| Soft fill (4×4 panel) | ~2,000 lx at 2m | Area light 50×50 cm · ~500 W | Physical Area Light 50×50 cm · 3,000–5,000 lm | Rect Light 100×100 cm · ~3,000 lm |
| Emissive neon | Practical neon 2,000–5,000 cd/m² | Emission mat 1,000–5,000 W | RS Light Material 2,000–5,000 nits · Affect GI on | Emissive 2,000–5,000 nits · GI enabled |
| Depth of field | f/1.4 = shallow, f/11 = deep | Thin Lens f-stop + focal length | Physical Camera f-stop + focus dist | CineCam f-stop + Focus Distance |
| White balance | Kelvin dial or preset | WB K in Imager node | RS Camera WB or Post FX node K value | Post Process → White Balance Temp |
| IES fixture profile | Use real fixture file | IES Photometry in Spot light | IES Profile in Point / Spot light attrs | IES Texture in Spot / Point light |
| Interior GI boost | Bounce cards / kickers | Increase bounce count; use portal geometry | Portal Light at window openings; raise GI bounces | Lumen Scene Detail / Quality settings; add Sky Light |