Continuous Light Exposure Calculator
Calculate exposure settings for continuous LED or tungsten light from lux, ISO, and aperture.
Get shutter speed for any video or photo workflow.
Continuous lighting is judged in lux, the SI unit for incident light on a surface. A camera, by contrast, thinks in EV (exposure value), the photographer’s logarithmic stop count. Translating between the two is the daily job of every gaffer, cinematographer, and product photographer who works with LEDs.
The conversion is built into the calibration of every light meter. The ISO and ANSI standards put it like this:
EV at ISO 100 = log₂(lux / 2.5)
So 25 lux is EV 3.32 at ISO 100, while 25 000 lux (a sunny midday open shade) is about EV 13.3.
To turn EV into camera settings, the relationship is:
EV = log₂(N² / t)
where N is the f-number and t is the shutter speed in seconds. Bumping ISO from 100 to a higher value adds log₂(ISO/100) extra stops you can absorb, so the working formula at any ISO is:
t = N² × 2.5 / (lux × ISO/100)
The math says everything you need to know about LED video work in one line. Halve the light and you double the shutter time, lose a stop on the f-number, or push ISO by a stop. Pick whichever penalty you can live with.
Some real numbers worth remembering. Indoor home lighting runs about 100 to 300 lux. A single 60 W LED panel a metre from your subject is roughly 1500 lux at the subject. Daylight through a window can hit 5000 to 10 000 lux without trying. Direct midday sun outdoors is around 100 000 lux, which is also where the Sunny 16 rule comes from: f/16 at 1/ISO seconds gives correct exposure at that level.
Two practical points. First, lux is what you measure with an incident meter pointed at the camera; what your subject reflects back is luminance, a different number that depends on surface tone. Calibrate your meter before a long shoot, especially with mixed-spectrum LEDs that can fool the photodiode. Second, video work is constrained on shutter side. The 180-degree rule (shutter time equal to half the frame interval) gives natural motion blur, so your free variables for video are aperture and ISO, not shutter speed. Photo work has the full triangle.
Why this matters more than it used to. Cinema LEDs are getting bright fast: a single Aputure 600d throws roughly 10 000 lux at 3 m, which is enough to overexpose at the 180-degree shutter and base ISO unless you stop down. Knowing the EV math means you arrive on set with the right ND filters and the right f-stop already in mind, instead of guessing through three test takes.