FWIW, I've found that most common cameras in the 720p-5MP range switch from day/color mode to night/bw mode in the range of 15-20lux.
If you want to try and maintain color images, I'd suggest general illumination of 20lux or more. If you want to get a good night time image I'd suggest general illumination of 10lux or more. Anything less than 5 lux of general illumination is unlikely to yield very usuable images.
People sometimes confuse lux readings in "open air" with minimum lux ratings on camera spec sheets (eg: a .1 lux camera). The spec-sheet reading is usually not as useful as it seems, but at the very least it is referring to the light level hitting the camera sensor.
Cameras see light reflected off objects. Object reflect a portion of the light hitting them, for people dressed in cotton clothing the reflectivity is usually around 10-20%. Light also dissipates over distance. If you have a person 100' away standing under a light that is providing 5 lux of illumination in the general scene, that person will be reflecting about .5-1lux of light back toward the camera (or in any general direction). That reflected light dissipates over distance, and the camera is not able to capture 100% of the light reaching the lens (lens quality, aperture, sensor quality, etc.).
There is no easy way to measure light reaching the camera from a given object, holding your lux meter next to the camera lens only tells you about the general illumination right at the lens. There are lots of variables, but you will end up needing ~100x the low-light spec of your camera at the target to get a "good" image.
To help complicate the lighting design, you'll find that most lamps are rated in lumens, not lux. You can't directly convert one to the other without some additional details (which are nearly impossible to get). Lumens is the *total* light output of the illuminator. Lux is the amount of light hitting a defined target area. Think of it like a maglight with an adjustable "focus". You switch the light on and the bulb lights up, it's putting out "X" lumens (lets say 500). Twisting the end of the maglight doesn't change the amount of light the bulb is producing, but it focuses that light in a spot (high LUX, maybe 500?) or in a floodlight pattern (low lux, maybe 80?). Light manufactures can't give you a lux rating because they don't know over what area/distance from the lamp you'll be measuring lux, but they can tell you the total amount of illumination produced by the bulb (lumens).