Introduction
The Lighting Power & Intensity calculator converts wattage to lumens using a source's luminous efficacy, then calculates illuminance in lux at any source-to-subject distance using the inverse square law. It returns total lumens from the source, lux at the subject, coverage area at the given distance, and the exposure value (EV) at ISO 100 so you can connect a light source's output directly to your camera's exposure settings. Presets cover LED, tungsten, HMI, and fluorescent sources.
What This Tool Calculates
Luminous flux (lumens) = Wattage × Efficacy (lm/W). For a source with a defined beam angle θ, the illuminated area at distance d = π × (d × tan(θ/2))². Illuminance (lux) = Lumens / Area, following the IESNA photometric calculation standard. Exposure value at ISO 100 = log2(Lux / 2.5). Worked example: 1200W HMI, efficacy 95 lm/W, 60-degree beam. Lumens = 114,000. Area at 5m = π × (5 × tan(30°))² = 26.2 m². Lux = 114,000 / 26.2 = 4,351 lux. EV = log2(1,740) ≈ 10.8 — equivalent to f/4 at ISO 1600, 1/50s.
The Formula and How It Works
A gaffer needed a 1200W ARRI M18 HMI to expose correctly at T4, ISO 800, 1/50s (EV 9.5). The calculator showed 4,351 lux at 5m (EV 10.8) — 1.3 stops over. Moving to 7m reduced lux to 2,225 and landed at EV 9.8. For a product tabletop commercial requiring 1,000 lux at 0.8m, a 200W LED panel (130 lm/W, 45-degree beam) produced 1,820 lux — 0.86 stops over, solved by moving the panel to 1.05m. For a noir short film, three 100W tungsten A19 practicals (14 lm/W, combined 300W) produced 62 lux at 3m — confirming a fourth practical was needed to reach the target 80 lux fill level.
Real-World Examples
Common Film Light Output Reference
Tungsten 1K Fresnel: 14,000 lm, ~792 lux at 3m (60° beam). HMI 575W: 54,625 lm, ~3,086 lux at 3m. HMI 1200W: 114,000 lm, ~6,440 lux at 3m. LED Panel 100W (130 lm/W): 13,000 lm, ~735 lux at 3m. LED Panel 300W: 39,000 lm, ~2,204 lux at 3m. Fluorescent 4-bank 800W (80 lm/W): 64,000 lm, ~3,617 lux at 3m. LED efficacy varies enormously by product quality (60–150+ lm/W); always use the manufacturer's published lumen figure.
Pro Tips and Common Mistakes
| Detail | Value |
|---|---|
| Lux is a point measurement at the center of the beam. | |
| At the beam edge, lux drops to roughly 50% of center. | |
| Account for this when placing lights for wide-area illumination. | |
| For softboxes and large diffused sources, use 90–120 degrees as the effective beam angle. | |
| The inverse square law is your fastest on-set mental shortcut: doubling the distance quarters the lux; halving the distance quadruples it. |
Pro Tips and Common Mistakes
Pro Tips
- Connecting a light source's wattage to the actual lux at your subject — and from there to f-stop and ISO — saves the gaffer-DP negotiation time and eliminates the guesswork of whether a given fixture will produce enough light at the planned working distance.
- Run the numbers before the lighting truck arrives..
Common Mistakes
Frequently Asked Questions
How do I convert lux to f-stop?
EV at ISO 100 = log2(Lux / 2.5). Each additional stop of ISO halves the required lux. At ISO 800 (3 stops above ISO 100), divide your lux value by 8 to get the ISO 100 equivalent, then find the corresponding f-stop from an EV table.
What is the difference between lux and lumens?
Lumens measure total light output from a source regardless of distance or direction. Lux measures illuminance at a surface: 1 lux = 1 lumen per square meter. A source's lux value changes with distance; its lumen value does not.
How much lux does a typical film set require?
Indoor narrative: 800–2,000 lux at the key light position for ISO 800–3200. Exterior simulation with HMI: 4,000–10,000 lux to match natural daylight at f/4–f/8. Tabletop commercial at macro: 500–1,000 lux depending on aperture.
Does color temperature affect lux?
Color temperature does not directly affect lux measurement, since lux is photopic (weighted to human eye sensitivity). However, cooler sources like HMI and daylight LED typically have higher luminous efficacy than tungsten for the same wattage.
Start Calculating
Use the calculator above to run your numbers before your next production.
