the key number is microns per pixel on the CCD/CMOS camera chip. the /good/ low light cameras such as the Dahua 5442 series currently have 1/1,8" chips, these are about 9mm diagonal, or 7.11 x 5.33mm, and at 4MP with 2688x1520 pixels, the pixels are about 2.65 microns square. a 4K camera is more likely to be a 1/3" which is 4.8x3.6mm, and at 3840x2160 has 1.25 micron square pixels. a 2.65 micron pixel has 4.5 times the surface area of a 1.25 micron pixel, hence is 4.5 times more sensitive. that is over 2 f/stops for the photographers in the crowd, or the difference between ISO 400 and ISO 1600 film. with another 1/6th stop on top of that, heh (for that extra .5)
a /really/ awesome low light camera would have a "micro 4/3rds" (17x13mm) or even a 35mm FF sensor (36x24mm) but those are seriously /expensive/ and also require much larger lenses and camera bodies. we use sensors like that in astrophotography for /really/ low light work but the cameras cost $$ 4-5 digits. astrophotography cameras are often built with Peltier coolers to keep them as cold as possible to reduce the noise... but for security cameras, you do NOT want the long exposures of AP so thermal noise isn't as big a deal (an astrophotography exposure might be 5 minutes per image, while for security you want 1/60th or shorter to freeze motion blur).
btw, I have the IPCT version of the HiKvision 1/1.8 NITECOLOR camera, and indeed it can do color at night with very little light, but instead of the usual IR illuminator, it has a pair of warm white LED flood lamps. Its currently mounted as my high driveway overview camera... I'm trying to decide how I want to light my driveway so I can shut these off, thinking maybe enough of those solar charging garden lights will do, each carefully masked with some black tape so they don't glare directly into the camera. I'd like to swap it out for the Dahua equivalent that has IR filtering with an IR LED and add some aux IR lighting to cover deeper. In particular, I want some light on the edge of the woods that are nearly completely dark in the far background left.
