A lux is a unit of illuminance: one lumen spread over one square meter. A camera lux rating states the lowest light level at which it still produces an acceptable image, but only under the shutter, gain and aperture settings used for the test, which datasheets rarely state.
Lux figures are the most quoted and least comparable camera specification. Two cameras claiming the same number can behave very differently at dusk.
What the number hides
A very low lux figure may come from a slow shutter that smears motion, or from digital gain that fills the frame with noise. Neither helps identify a person.
A better comparison
Compare sample night recordings at a realistic frame rate, and ask what shutter and gain the manufacturer used. Color performance and IR range matter separately.
Related:Commercial security camera systemsGlossary: PTZ camera systems