Distance
Another key ingredient of this technique is distance. To achieve the desired shot, you need to properly coordinate your lighting with the background. By anticipating how much light is lost over distance, you will be able to figure out the best position to place your light. The idea is to find that sweet spot, where the light hits your subject perfectly and doesn’t reach the background. To do this, simply adjust your shot by either moving your light back and forth, or by bringing your subject further away from the background. The single most important rule of low key photography is to not let the light reach your background, as this is how the effect is achieved. If by chance your space is limited, try moving the light to the side of your subject, making sure that focus of your shot is still well lit. This will darken the background even more, and will add drama to your composition.