Photography Basics - Inverse Square Rule

Words by Scott Bourne - A Platypod Pro
Edited by Eryka Bagwell

If you want to really understand light and how to use it in photography, start by understanding the inverse square rule (also sometimes called the inverse square law.)

First we'll give you a semi-official explanation which might make your eyes glaze over, but don't worry, we'll keep the whole post short and sweet and sum up with something we are sure you can understand. Then go practice.

The inverse square rule in photography is a principle that explains the relationship between the distance from the light source and the brightness of the light falling on a subject. It states that the intensity of light from a point source decreases as the square of the distance from the subject increases.

In simpler terms, the inverse square rule means that when the distance between the light source and the subject is doubled, the amount of light that reaches the subject is reduced by a factor of four (2 squared). Similarly, if the distance is tripled, the light reaching the subject is reduced by a factor of nine (3 squared), and so on.

This principle is essential for photographers as it affects how they set up their lighting and determine the exposure settings for a particular shot. By understanding the inverse square rule, photographers can adjust the distance and intensity of their light sources to achieve the desired effect and create well-lit images.

So what does all this really mean? Assuming you're a beginner we'll start with the simplest explanation and ask you to practice it for yourself. If you move your light farther away from the subject, the light will diminish in brightness. Simple. Move farther away, and your illumination grows dimmer.

The rule has one simple job. It is to tell us how much the light diminishes when we move it further away or closer to the subject. Doubling our distance reduces the light falling on the subject by 25%. If you only remember one key thing about this - make it the following.

The Inverse Square Rule is all about distance.

Now go practice with a simple flash light and a model or a prop and you'll know much more about light than most of your friends who want to become serious photographers.

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