Yes, a camera with a built-in infrared (IR) LED is able to capture images in complete darkness. However, the images captured during darkness will be in mono colour (black and white) only.
Today’s advanced technologies have resulted in more and more security cameras becoming increasingly capable of capturing colour images in what’s often described as ‘near darkness.’ Cameras are increasingly outperforming the human eye when it comes to seeing in the dark.
Light sensitivity in CCTV cameras is stated in LUX. In theory, the lower the LUX measure the more light sensitive the camera is. This single measure is useful in a small, controlled environment but not so much when a camera is covering a large outdoor space with scene complexity and environmental conditions playing a part. Therefore, in many cases, you cannot just simply rely on the LUX information in a data sheet.