Chiaroscuro lighting accentuates the focal point of the composition by bathing it in light and surrounding the focal point by darker recesses. The Italian word ‘chiaroscuro’ means light and dark, and the alternative name of ‘Rembrandt’ lighting comes from the fact that he is the foremost artist who used that lighting effect in his paintings.
The contrast between light and dark areas also accentuates the three-dimensional appearance of the subject.
In photography the chiaroscuro lighting effect is straightforward to achieve with window light, because window light is directional. In the northern hemisphere the ideal window is one that faces north, away from the direction of the sun, because the light is less contrasty. That means that the intensity of the light from the light parts to the dark parts is less than if part of the subject was lit with full sun.
However, if the subject is placed very near the window, the light fall-off may still be too rapid because light always falls off most rapidly nearest the light source, Near the light source there is a dramatic decrease in the intensity of the light with each step back into the shadows.
If the subject is placed well into the room, say twenty feet from the window, and is then moved another foot further away from the window, the fall off of light caused by moving that small extra distance from the light source will be small because the light has already spent its power penetrating that first twenty feet.
The downside of moving a subject far from the light source is that it is simply darker overall. That is not a problem if you are Rembrandt because you can paint your subject as you like. With photography, it’s a bit trickier because you have to have enough light. If there isn’t enough light then you have to change the shutter speed, the aperture, or the ISO. You are probably already going to be using the maximum aperture because you want good subject separation from the background.
And you don’t want to bump up the ISO if you can help it because you want the cleanest image you can get, with little noise.
The answer is fast lenses. It’s what you pay for. A lens that opens to f 1.4 is worth having if you do a lot of this kind of work. That said, most camera manufactures make a normal (50mm full-frame equivalent) lens with an f1.8 maximum aperture, and that’s a pretty good choice. The f1.4 lens that springs to mind is the Fuji 35mm f1.4. To know more about lens apertures, read the article by following the link.
Chiaroscuro lighting can be too dramatic for some subjects. One way to overcome the problem of too much contrast across the subject is to place the subject near the window to get plenty of light on the subject. Then use a reflector on the shadow side to bounce light back to reduce the contrast.