The Street Looked Different After Sunset
A DP scouts a residential block at noon for a 24fps night exterior. The plan puts 2 actors 12m from camera, with a streetlamp motivating the key. The rental order includes one hard source, 2 battery LEDs, 45m of feeder, and a small generator.
At the night scout, the LED streetlamp measures brighter than expected and spills green onto the actors. The chosen key cannot create the planned 2-stop separation after diffusion. Moving it closer fixes output but puts the stand inside the wide shot.
This post shows how to measure ambient exposure, define a lighting ratio, read manufacturer photometrics, and convert the package into a safe power plan.
The method uses incident readings, the inverse-square relationship, and published fixture data. It replaces fixture folklore with measurements from the actual location and modifier package.
The Exposure Math That Drives the Package
Start with camera settings and an incident meter at the actor mark. A cine meter can display a T-stop after you enter ISO, frame rate, and shutter angle. Sekonic's on-set metering guide explains why incident measurement quantifies light falling on the subject rather than reflected scene brightness.
Exposure Value at ISO 100 follows EV100 = log2(N² / t), where N is the f-number and t is exposure time in seconds. At 24fps with a 180-degree shutter, t is about 1/48s. T2.8 therefore corresponds to about EV100 8.6 in camera-setting terms.
For incident illuminance, a common ISO calibration gives lux ≈ 2.5 × 2^EV100. Meter constants differ, so use the same calibrated meter for scout and shoot. Do not mix an estimated lux value with an unrelated camera waveform reading.
Lighting ratio needs equally careful language. If ambient measures 25 lux and you want the final key-side level 2 stops higher, the final level is 25 × 2² = 100 lux. The added fixture must contribute about 75 lux, not 100, because ambient remains present.
Distance changes direct illuminance approximately by the inverse-square relationship: E2 = E1 × (d1 / d2)². A head that produces 1,200 lux at 5m yields about 300 lux at 10m before diffusion, beam changes, or atmospheric loss. Manufacturer photometrics beat a wattage comparison because optical efficiency and beam angle vary widely.
Three Night Exterior Plans
1. Residential Dialogue Scene
A Sony FX9 at ISO 1600, 24fps, 180 degrees, and T2.8 frames 2 actors under a 4,000K streetlamp. Incident ambient is 20 lux. The DP wants the key side 1.5 stops above ambient, or about 57 lux total. A diffused source adds 37 lux at 9m, while a negative-fill frame controls the opposite cheek.
2. Rural Horror Insert
A Canon C400 at ISO 3200 and T2 records a hand finding keys beside a stalled car. Ambient is below the meter's useful range, so the crew builds the level from zero. Headlights motivate a hard backlight, while a battery LED through 1/2 grid supplies the hand. The gaffer meters the final stop rather than assigning a fictional rural EV.
3. City Walk-and-Talk
An ARRI ALEXA 35 at EI 1600 follows 2 performers past shop windows. Existing levels vary from 80 to 500 lux within one block. Instead of overpowering the street, the crew maps exposure zones, dims a walking LED key, and rehearses iris pulls. The lighting plan controls faces while preserving practical highlights.
Current Fixture Data for Long Throws
Published photometrics let you shortlist a head before a rental test. ARRI lists the following 5,600K native-hard figures for its current modular SkyPanel X family.
| Fixture | Power draw | Published output at 10m | Native hard beam |
|---|---|---|---|
| SkyPanel X21 | 800W | 4,800 lux | 11 degrees |
| SkyPanel X22 | 1,600W | 9,600 lux | 11 degrees |
| SkyPanel X23 | 2,400W | 14,400 lux | 11 degrees |
Source: ARRI SkyPanel X technical data, accessed September 2026. These are maximum native-hard readings, not soft-light results. Use ARRI's current Photometrics app for attachment, distance, CCT, and beam-specific values.
Build the Night Exterior Plan Step by Step
- Scout after dark at the scheduled hour. Record the date, weather, lunar conditions, municipal timers, and every practical that appears in the planned coverage.
- Match the production camera settings. Enter the working ISO, 24fps or chosen frame rate, and actual shutter angle into a cine meter. Measure at every actor mark with the lumisphere oriented consistently.
- Create an exposure map. Put ambient lux, meter T-stop, color reading, and waveform notes beside each blocking position. Flag practicals that flicker or cycle.
- Set the final key-side level. Choose the desired stop difference from ambient. Calculate
final level = ambient × 2^stops, then subtract ambient to find fixture contribution. - Read photometrics with modifiers included. Check the exact reflector or optic, distance, CCT, beam angle, and diffusion. If the manufacturer lacks modifier data, test the rental unit with your frame.
- Check position and falloff. Plot stands outside every lens angle. Recalculate output if the wide shot forces the head from 7m to 12m.
- Audit color and flicker. Measure streetlights, signage, vehicles, and architectural LEDs. Decide which sources stay mixed, which get corrected, and which get flagged.
- Convert fixtures to electrical load. Enter nameplate watts and quantity in the Lighting Power Calculator. At 120V, an 800W fixture draws about 6.7A before considering other loads.
- Add distribution and weather controls. Specify cable gauge, connector system, ground-fault protection, rain cover rated for the fixture, stand ballast, and a qualified set electrician.
- Run a camera and meter test. Photograph faces, wardrobe, wet pavement, and bright signs. Save false-color or waveform references for the shooting crew.
The finished document is an exposure map tied to a fixture list, rigging plan, and electrical schedule.
Pro Tips and Common Mistakes
Pro Tip: Test the light through the production diffusion. A grid cloth can change both output and beam shape, so a bare-head photometric number cannot approve the final placement.
Pro Tip: Map the background separately from faces. A dark 30m background can read naturally while the foreground sits at key exposure. Lighting every surface to one stop wastes output and flattens depth.
Pro Tip: Photograph meter placement. A reading at chest height under a streetlamp may differ sharply from one at the actor's eyeline 60cm away.
Common Mistake: The package is chosen by electrical wattage. The fix: compare measured lux at the required distance, beam, CCT, and modifier, then calculate watts for power distribution.
Common Mistake: The generator is sized from fixture totals alone. The fix: use equipment nameplates, ballast or power-supply requirements, continuous-load limits, cable losses, and local electrical rules with a qualified electrician.
Frequently Asked Questions
How much light do I need for a night exterior?
The answer starts with the meter reading at the subject, not the location label. Define the final T-stop and contrast ratio, then calculate the fixture contribution after ambient light.
Can a phone lux-meter app replace a cine meter?
A phone can compare relative levels during an early scout. Sensor placement, diffuser design, and calibration vary, so verify the final package with a calibrated incident meter such as the Sekonic L-858D and the production camera.
Why does moving a light back reduce output so quickly?
For a compact source in free space, doubling distance reduces illuminance to roughly one quarter. Real fixtures depart from the simple model because reflectors, lenses, and beam angles shape the output.
Should I plan night exteriors with EV or lux?
Use the cine meter's T-stop for exposure decisions and lux for photometric comparisons. EV can connect the systems, but inconsistent ISO references create easy 3-stop errors.
Can LEDs replace HMIs for every exterior?
No fixture category wins at every throw, beam, color, weather rating, and power limit. Compare current heads using manufacturer data and a rental test rather than lamp technology alone.
Tools for Exposure, Color, and Power
Set camera parameters in the Exposure Triangle Calculator, total the electrical load with the Lighting Power Calculator, and plan gel shifts in the Color Temperature Calculator. The guides to mixed lighting and shutter-angle choices cover the next decisions.
The Rental Order Is the Result, Not the Starting Point
A reliable night package comes from measured ambient, a stated ratio, modifier-aware photometrics, and a checked electrical plan. This method does not replace a gaffer, set electrician, weather review, or location test.
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On your hardest night exterior, which changed the package most after the scout: throw distance, practical color, wind, or available power?
