Photography Cheat Sheet: Inverse Square Law of Light for Dummies

If the Inverse Square Law and how it pertains to light are all new to you, we have a photography cheat sheet that explains how it works and affects your photography.

At some point in your photography journey, the topic of Inverse Square Law will pop up and probably perplex you. While it sounds very technical and intimidating, it actually pays to know how it affects the way your subjects or scenes are lit. We have just the tips and visual guide for you in today’s photography cheat sheet.

First, let’s turn to physics for the actual definition of the inverse square law. According to this lesson from John Peltier, the law says that the intensity of a force (in this case, light) is inversely proportional to the square of the distance from that force. Basically, it describes the relationship between distance and the brightness of light. This law applies to any kind of light source, so learning about this should give you an idea on how to work with flash and studio lights better.

The cheat sheet above by tinyprints.com, we see a visualization of the inverse square law to show that the intensity of light drastically drops off as you move away from the source, then fades out. Shooting with flashes and other studio lights make a good example of how the inverse square law applies to photography. When you’re working with flash, of course, you want your subject to be evenly lit. This often tricky when you have several subjects or even a wide area to photograph in the studio, as demonstrated in the lesson mentioned by John Peltier. Put the light too close and only the people close to the light source will be illuminated. The solution is to move the light source further away and increase the power.

If you want to use dramatic falloff to light up only your subject and not the background,  decrease your flash power and place the light source as close as possible to the subject. Adjust the flash power as necessary to get the effect you want.

Learn more about this topic from a simple but helpful tutorial by Matt Day.

Need more photography tips and tricks like this? Don’t forget to check out our photography cheat sheet collection to find more that will come in handy for your next shoot and projects!