Choose a fixture and optic, then enter your planned throw and camera settings. Use the estimated lux, foot-candles and f-stop to see whether the light will give you the exposure you need.
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1. Choose a light
2. Set planned camera exposure
Meter calibration (optional)
The default uses a raised-dome reference to convert published lux into an estimated aperture.3. Set the light position
Camera settings are shared. Each light is estimated independently at its own distance and output level.
4. Choose fixture B
Choose a second fixture. Both lights use the same camera settings.
How the estimate is calculated
Manufacturers and other documented sources publish illuminance in lux at specified distances and optical configurations. This tool uses those figures, interpolates between published distances when required, and estimates an incident-meter aperture from ISO and exposure time. Raised dome mode uses calibration constant C = 340; flat diffuser mode uses C = 250, as specified in Sekonic incident-meter documentation. The main result uses conventional f-stop marks plus tenths of a stop; the next line gives the nearest standard lens marking.
Single-fixture readings are for one light pointed at the subject under the manufacturer’s test conditions. The calculation does not add ambient light, account for another fixture, or predict exposure after diffusion, bounced light or other unlisted modifiers. The result is an incident-meter exposure estimate, not a direct measurement through a specific lens. For cine lenses with T-stop markings, the same indicated exposure value is a useful starting point on the T scale; an exact physical f-stop-to-T-stop conversion depends on lens transmission.
Before relying on the reading
- Match the attachment. Bare-bulb readings cannot be used for a softbox, fresnel, lantern or reflector unless that exact accessory is listed.
- Check the distance. At a published throw, the calculator uses the chart reading. Between chart points it interpolates. For a compact hard source, a shorter or longer throw uses the nearest published lux value multiplied by (published throw ÷ planned throw)². Keep the same optic, focus and beam position. Close to a large lens or reflector this is a rough planning estimate. For tubes, large panels, softboxes and other setups without a reliable falloff model, the nearest published reading is shown as a reference.
- Expect variation. Beam distribution, subject position, meter dome direction, ambient light, dimming curves, power mode, unit variation and lens transmission change the result. Use an incident meter or camera tests for final exposure.
- Compare like for like. Different reflectors, Fresnel settings and operating modes change center-beam lux. Check distance, CCT, attachment and normal/high-speed mode rather than comparing wattage alone.
Common questions
Where do the photometric measurements come from?
Each selected fixture links to its supporting data source. Most use manufacturer-published photometric tables. Some use manufacturer datasheets hosted by third parties, and a small number use third-party equipment listings. For example, the original 2011 ARRI L7-C readings apply to boost/active cooling, not later L-Series light engines or passive cooling. Godox MG1200R and MG2400R normal and high-speed measurements are distinguished in the setup selector; an ambiguous MG2400R GR15 table entry is not offered. Where the fixture page carries the table, follow Fixture details to see its readings and references. FVL has not physically measured these fixtures. Measurements can differ by revision, optical attachment, CCT and operating mode.
Why does the dome mode read differently from flat-diffuser mode?
Incident meters are calibrated for their light-receiving attachment. Sekonic specifies C = 340 with a raised Lumisphere and C = 250 with a flat diffuser. At the same illuminance, the difference is approximately 0.44 stop. Use the dome setting when comparing with a conventional incident-light meter; physical meter orientation and incoming beam shape can still affect the reading. See the Sekonic calibration specifications.
How do I read the displayed meter aperture?
For example, “f/16 + 0.5 stop” means halfway between f/16 and f/22 in exposure, not f/16.5 as a mathematical aperture number. The nearest lens marking is shown separately in full, half or third stops. A lens may not offer all of those markings.
Will I actually get the displayed f-stop?
Not necessarily. This is a direct-light planning estimate based on the manufacturer’s stated illuminance. Bounce, added diffusion, other lights and off-axis placement can change the exposure on the day.
Why can I only choose certain colour temperatures?
Only settings with published photometric figures are included. Output can change with colour temperature; the calculator does not assume that every CCT produces the same lux.
What does a one-stop difference mean in a comparison?
One stop more light means approximately twice the illuminance at the subject. At the same ISO and shutter, this corresponds to an aperture approximately 1.4 times the f-number, not twice the f-number. The comparison reads each lamp separately and does not sum their output.
Can I use a softbox or another modifier?
Only when a manufacturer has published readings for that exact light-and-modifier combination in the setup menu. Otherwise use the tool to evaluate the source before modification, then meter the altered setup. A universal softbox light-loss factor would not be reliable.
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