Day-Night CCTV cameras must have reasonable light to show a picture. Low light BW is always better, then BW, then EXVIEW colour followed by colour. Night view cameras with IR will show pictures in no light using the range of IR. The picture will be BW under of range of IR.
IR Cameras are an excellent way of providing a picture in poor light. These can be supplemented by the use of extra IR lights.
At all times cameras will work in color if WHITE light is used, ie a light activated by use of PIR sensor.
