Light at distance
Use a fixture's published photometric data to see what it delivers where you put it. Enter the lux value and the distance it was measured at, the beam angle and the distance to your subject; the calculator gives the light on the subject in lux and foot-candles, the diameter of the light pool and the stop at your ISO and shutter speed.
Use it in prep to choose fixtures and positions before the lighting truck is loaded.
How to use it
- Fixture output: lux at a stated distance from the manufacturer's photometric chart, for the beam angle or lens you plan to use.
- Beam angle: sets the size of the light pool.
- Distance to subject: in meters or feet.
- ISO / EI and shutter speed: for the stop.
Example
A fixture rated 5000 lux at 3 m with a 30° beam gives about 1800 lux at 5 m, in a pool about 2.68 m across. At ISO 800 and 1/48 s that is about T11.
Good to know
Light falls with the square of distance for focused, hard sources; large soft sources fall off more slowly up close. The stop uses a meter calibration constant of C = 250, as in the light meter tool.