If you remember one thing from physics class, make it this. The Inverse Square Law states that the intensity of light is inversely proportional to the square of the distance from the source.
In English? If you move your light 2x further away, you don't get 1/2 the power. You get 1/4 the power. Light falls off drastically fast.
Why This Matters
Have you ever taken a portrait where the subject is bright but the background is also bright and distracting? That's because the light source was too far away.
To create a moody image (black background):
- Bring the light very close to your subject.
- Move your subject away from the background.
- Because of the Inverse Square Law, the light will hit your subject powerfully but will have lost almost all its energy by the time it reaches the background.
Hard vs. Soft Light
This law also affects softness. The closer a light source is to a subject, the larger it becomes relative to them. Larger light sources creating softer shadows.
The Formula
Next time you want drama, don't just dim the light. Move it closer.