Sharpen the Shadow Lines
In film noir, the shadows are like characters in the story. It's important for those shadows to be sharp and distinct. This helps the viewer create a clear mental image of the object casting the shadow, like a gloved hand holding a knife or gun from somewhere outside the frame.
To create sharp, clean shadows, use a single point of light. Some commercial lights have reflective surfaces that break up the light and cast it in multiple directions. This can cause multiple, overlapping shadows at different levels of contrast. A single point of light casts a single shadow that's easier to position and bring in focus.
A cheap way to get a single point of light is to use a single uncovered incandescent bulb. You could put this on a typical household lamp and remove the lampshade. For something brighter, you could purchase an inexpensive floodlight or shop light that uses the same type of incandescent bulbs you'd use in lamps, just with a higher wattage (like 150 watts). If the floodlight's reflective fixture breaks up the light too much, you can remove it so all you have left is the socket and cord for the light.
When a single light isn't enough for the entire scene, you can add more lights without sacrificing the sharp shadow lines. To do this, just make sure the light rays are all going in the same direction. If the rays go in different directions, shadows will appear in different places, and no one shadow will have the nice sharp contrast you need. Take time to study the light of your shot as you determine where to put each additional light, and remember that you might have to reposition all the lights after adding each one.
After you place the lights, you'll need to set your camera to capture the scene in true film noir style. Our next tip is all about using the camera settings to enhance the mood of the shot.