LightCalc v3 — Footcandles on set

Stage 1: Light Source

Fixture

Quantity

Beam Angle (°) ?Half-angle at 50% intensity (FWHM). Open face ≈ 120°, Fresnel spot ≈ 15°, Fresnel flood ≈ 60°, Par narrow ≈ 12°, Par wide ≈ 30°. Determines how much of the beam hits the diffuser.

Beam Pattern ?Gaussian: hot center, soft edge. Flat Top: uniform panel-style output. Cosine: classic tungsten/HMI falloff. Affects diffuser illumination uniformity.

Tilt (° off-axis) ?Fixture tilt relative to diffuser normal. 0° = perpendicular (aimed straight at diffuser). Applies cos(tilt) to effective illumination.

Modifier 1

Type

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Distance 1

Fixture → Diffuser (ft) ?Distance from the fixture/modifier to the diffusion frame, in feet.

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Stage 2: Main Diffuser

Diffuser type ?Grid cloth and diffusion reduce light output. Transmission values: ¼ Grid 85%, ½ Grid 50%, Full Grid 25%, Light Grid 35%, Opal 30%.

Diffuser width (ft)

Diffuser height (ft)

Gel / ND ?Optional gel or ND filter applied after the diffuser. Multiplied into the transmission chain.

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Distance 2

Diffuser → Talent (ft) ?Distance from the diffusion frame to talent mark, in feet.

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Talent

Advanced

IES Photometric File ?Load an ANSI/IES LM-63 (.ies) file for accurate candela distribution. Replaces the simple lux@1m approach for Mode B when loaded. Load IES file

Diffuser scatter ?How directional is the diffuser? Grid cloth scatters less than opal. 0% = fully Lambertian (light scatters equally forward), 100% = fully specular (light passes straight through). Interpolates between area-source and point-source models.

Lambertian Specular 0%

Diffuser coverage

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Results — Talent Position

fc (Practical) ?Gaffer approximation: treats the rig as a modified point source. Total distance = fixture→diffuser + diffuser→talent, then inverse-square with diffuser transmission loss. Quick and useful on set.

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fc (Physics) ?Area source model: calculates lux hitting the diffuser, applies transmission, treats the lit diffuser as a Lambertian emitter, and integrates illuminance using projected solid angle. More accurate for large, close sources.

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Delta

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T-stop guide ?Nearest T-stop for the selected ISO. EV100 = log₂(fc × 10.764 / 2.5).

ISO

Distance Falloff

Background / Separation (optional) ?Enter a horizontal distance from talent (same height) to calculate light falloff for background or separation lighting.

Horizontal distance from talent (ft)

Saved Rigs