Understanding lighting is crucial. One fundamental concept is the inverse square law.
Coming to you from John Gress, this enlightening video explores the inverse square law. The inverse square law states that the intensity of light decreases dramatically as you move the light source farther from your subject. For example, doubling the distance of the light from your subject reduces the light intensity to one-quarter of its original value. This rapid falloff is essential to understand for effective lighting setups.
This video explains how the inverse square law helps you control light falloff from your subject to the background. If you want a dramatic portrait with a well-lit subject and a dark background, place your light source close to your subject. The light will fall off quickly, leaving the background dark. If the background is too bright, move the subject and light farther from the background. Conversely, if you want a bright background and it's too dark, move your subject and light source closer to the backdrop.
In practical terms, understanding the inverse square law can solve common lighting issues. If your light is too bright at its minimum power, move it further away. If it's not bright enough at maximum power, move it closer. Moving the light closer not only increases its intensity but also softens it, as the light source appears larger to the subject.
To illustrate the inverse square law, Gress places a bare bulb perpendicular to a backdrop and photographs it at various distances. Every time he doubles the distance from the light, the light by three-quarters. However, as you get farther away, there's less difference in brightness between, say, 7 feet and 8 feet from the light source than 1 and 2 feet.
The demonstration continues with the light source 1 meter (about 3 feet) from the subject. The subject is well lit, and the background quickly falls into darkness. Moving the light source 2 meters away, the light becomes one-quarter as bright, so the ISO is increased by two stops to compensate. The background starts to brighten because the difference in distance between the subject and the background is less. At 4 meters (about 12 feet), the light on the subject and background are nearly the same.
In a close-up portrait example, Gress shows how light behaves differently based on distance. With the light close to the subject's face, there's a dramatic hotspot that quickly falls off into darkness. Moving the light further away, the light becomes more even across the face.
Understanding the inverse square law helps you master light falloff, intensity, and mood in your photos. This principle gives you greater control over your lighting setups, whether you're in a studio or on location. Check out the video above for the full rundown from Gress.
If you would like to continue learning about how to light a portrait, be sure to check out "Illuminating The Face: Lighting for Headshots and Portraits With Peter Hurley!"
Understanding this basic of "inverse square law" using flash/strobe lighting is necessary to photograph large groups/families/teams also. Even lghting of a group 3 to 6 rows deep is a real challenge, and a special skill set, indeed.