Most Nikon digital SLR cameras have a focus assist light that illuminates when you press the shutter button half way down to focus.
Some folks may think the light is too bright and don’t want to be intrusive, or not want to call attention to the camera or that they’re taking pictures. At other times you may be photographing subjects like a pet or animal, or even a baby and you don’t want them to be distracted by the light.
It’s easy to turn the focus assist light On/Off. Simply go into the custom settings in your camera’s menu and select the setting for the focus assist light and turn it off. If you want to use it later, go back to the menu option and turn it back on.