One of the Most Fundamental and Important Principles of Lighting

When you're new to lighting, the veritable plethora of principles, terms, and techniques can be a bit overwhelming, but there are a few fundamental principles that you should absolutely learn to ensure your understanding is secure. This great video talks about one of those principles. 

Coming to you from Aputure, this helpful video talks about the inverse square law and its effect on light falloff. One small correction: while the video says light intensity is equal to the reciprocal of the square of the distance, it actually means it's proportional to it. It's particularly important to understand this, as humans are in general absolutely terrible at intuitively estimating nonlinear phenomena such as this, and if you rely on your intuition when lighting a set, you might be thrown off by the behavior of the light. It's important to actively think through the lighting instead of relying on intuition. The more you practice lighting while keeping this principle in mind, the more you'll get used to it and be able to overcome the inaccurate heuristics your brain would normally rely on. Check out the video above for the full rundown and some great examples of the principle in action. 

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5 Comments

Blake Aghili's picture

Harvey? - Sorry brain is dead ! been a long day - the Headshot crew guy I mean , forgot his name!...
He has a youtube about inverse square law, that one is pretty good too .

It is *inversely* proportional - thus reciprocity is correct. Egads...

Alex Cooke's picture

Correct, I wasn't arguing that. I was arguing the use of "equal to" versus "proportional to." You can say it's proportional to the reciprocal of the square or inversely proportional to the square, but you can't say it's equal to.

The video addresses the presence of light without discussing the presence of shadow well enough in my opinion. I had expected to learn more about the dark side. (Insert Star Wars joke here.)

A subject closer to a light source will have a deeper shadow because the contrast of the illuminated side is greatest when your subject is closest to the light. As the subject distances themselves from the light, the illuminated side is smoother and less specular. Save for other light sources, the shadow side will be almost opaque when a subject is closest to a light. When you're further from the light source, the light is more present in space and not as linear. There's an attempt to reveal this but it's not documented with the images used. The background used is essentially a slice or cross section of the light.

I think a chief take away I had expected to be revealed is that the contrast of a light source decreases over distance. And secondly when light exists in space through dispersion it's available to be used by tools such as reflectors to be redirected at your subject as fill light.