Inverse square law sounds ridiculously complicated, doesn’t it? Luckily, it’s not as complicated as it sounds and as a photographer, you should know what it is and how to use it. Karl Taylor, a commercial photographer from the UK, shows you everything you need to know about the inverse square law and how to use it to your advantage in a short understandable video. (This is Part 1 of the video).

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…any physical law stating that some physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity.

That’s the exact wording of the inverse square law, but in this post, we’ll just take a look at what that scientific term specifically means for photographers.

The inverse square law actually determines two separate characteristics of the light:

  • The fall-off in relation to the distance
  • The power in relation to the distance

The setup

Karl does a nice experiment to show what the inverse square law means. He set up a camera on a tripod that is filming him and his model. At a 45° angle, a light is pointed at them.

inverse square law close

When the light is relatively close to Karl Taylor and his model, you notice a big difference in exposure between the two. Karl is way darker because of the greater fall-off at the lower distance.

inverse square law far

If you move the light further away, the difference in exposure becomes smaller, and as you can see, Karl and his model are almost equally exposed although the light is closer to his model. This is especially important if you light large groups of people, because you want to expose everyone properly.

The light is also getting harsher because is is becoming a smaller light source relative to the subject.

As mentioned this is only part one of the video. Now that you know the inverse square law of light, how can this help in your photography?

[via Karl Taylor, images via screencaps]