How the Inverse Square Law Can Make You Better at Lighting

Don't worry, this video isn't about all about math. Rather, it aims to give you an intuitive understanding of one of the most fundamental laws of physics related to photography and shows you why it's so crucial to have a solid understanding of how it works.

If you read a bit about cognitive psychology, you'll see that humans are really terrible at estimating non-linear phenomena, which is why stuff like the way light intensity changes with distance can throw us for a loop, particularly when we're first starting in photography. This helpful video from Joe Edelman will explain (in more practical, non-mathematical terms) how the inverse sqaure law works, what consequences it has on lighting for photographers, and what principles to keep in mind when you're shooting so you can get the shot you desire. While you can dive into modifiers and CRI and all sorts of things all day when it comes to lighting, if there's one principle that will have the greatest effect on your output, this is it; so, make sure you really know it as well as possible. 

Just a note, at 4:00, Edelman says at quadruple the original distance, the light intensity is 1/6th the original amount; it's actually 1/16th. Otherwise, the information is all quite sound and helpful!

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14 Comments

Agoston Zacs's picture

"Edelman says at quadruple the original distance, the light intensity is 1/6th the original amount; it's actually 1/8th."
The right is 1/16th, it was obviously a slip of tongue.

Alex Cooke's picture

Correct, thank you. I had two different values in my head and crossed wires.

Agoston Zacs's picture

Yes, it is 8 stops.

1/16 is 4 stops

Alex Cooke's picture

Correct, log2(16)=4

Agoston Zacs's picture

Sure, I was also mistaken for some inexplicable reason :)

Robert Nurse's picture

These lighting videos are always helpful to me. What I'd like to see included, however, is how the size of the light (with respect to the size of the subject) effects the final product. For example, small and close vs. large and close, small and far vs. large and far, etc.

jurian kriebel's picture

Found it so weird that he did not note that.

Mr Edelman is saying that the closer the light source is to the subject, the shadows are more harsh. Sorry but this is Wrong. the bigger the light source, the softer are the shadows. this is what i know, from thousands of photos i have taken. light source closer is bigger therefore softer shadows. Correct me if i am wrong.

Everything else I have read and seen agrees with what you're saying.

Agoston Zacs's picture

In my opinion both of you is right. The closer the lightsource the harsher are the shadows AND the bigger the lightsource is the softer are the shadows. The two statements do not contradict.

the bigger the light source in relation to the object - soft shadows. it is very very simple. and also easy to test. on camera flash gives harsh shadows while a soft box in the same distance give soft shaodws. period. :)

Nico Socha's picture

Yes he explained it wrong. If it was true the Sunlight would have soft shadows.

I'll stick to natural light and add a few more months to my life.