Now, don’t freak out! For some of you the words “Inverse Square Law” might bring back painful memories of that high school math class you thought was finally behind you, but we promise that it’s not that complicated. We will explain this concept using layman’s terms or as I like call them; “Pyeman’s terms”.
The Inverse Square Law can be simply understood if you keep these two things in mind.
- Your light loses power as you increase distance from the light to the subject.
- You will lose this light at a faster rate than you think.
For example, if you set up your light 1 meter away from your subject and you are getting 100% power flash hitting your subject. You move your light back 1 meter and now you’re 2 meters away. Does that mean you lost half your light, about 50%? It seems to be logical but it’s not the case. You actually lose 75% of your light. We can say this a different way. You only have 25% of your light intensity hitting your subject or ¼ of your light. Below, the chart is enlarged to help visualize this.
Before we move on, let’s quickly take a look at the actual formula.
Why is it called the inverse square law? Let’s break it down further step by step:
Simply put, inverse means the opposite of itself. You flip it. For example, 2 would be ½ and 4 would be ¼.
Simply put, square means a number multiplied by itself. For example, 2×2 or 10×10.
When we combine them, we get inverse square.
2 inverse is ½
½ squared is ½ X ½
And what is ½ X ½? It is ¼.
So 2 inverse squared is ¼. Another way to say this in terms of photography is that at 2 meters away you get ¼ the power. This is the inverse square law. That is how you figure it out. If you know the distance you are going to be from your subject, all you have to do is plug that number into the formula to find out how much light you will lose.
When looking at our chart you also notice something very interesting. From 1 meter to 6 meters, the percentage of light loss is dramatic. But from 6 meters to 7 meters is not as dramatic, it’s only .6%. Also from 7 meters to 8 meters, it’s only about .5%.
Knowing these basics, the inverse square law is used most when shooting large group pictures. It has a practical sense. If you place your light front and center of your group about 3 meters away, based on our chart and the formula you might think that the group will be getting 11.11% of your light and you will adjust accordingly (increasing the power). But only the individual at the center will be receiving 11.11%.
The individuals at the far corners of the group are going to be farther away than the one at the center. They might be 6 meters away from the light source thus only giving them 2.78% of the power. This creates a very unflattering and uneven light for group portraits. Because we know that light intensity has a less dramatic falloff at a greater distance, we have to pull the light source even further away to have even lighting among all the individuals.
The inverse square law is not as complicated as it sounds and knowing these fundamentals will benefit you greatly.
- 1.1 Lighting 101 Trailer 6M 13S
- 1.2 Chapter 1 Intro 1M 14S
- 1.3 Why Just One On-Camera Flash
- 1.4 5 Reasons to Use Flash 10M 43S
- 1.5 4 Common Flash Myths 7M 5S
- 1.6 What Makes Flash Challenging
- 1.7 Chapter 1 Quiz: Getting over the Fear, Hype & Myths
- 2.1 Chapter 2 Intro
- 2.2 Flash-Strobe vs. Ambient-Constant Light
- 2.3 Flash vs. Ambient Light Exposure
- 2.4 Flash vs. Ambient Demo
- 2.5 Flash and Ambient Balancing For Natural Effect
- 2.6 Assignment: Balancing Flash & Ambient for Natural Effects
- 2.7 Flash and Ambient Balancing For Dramatic Effect 4M 29S
- 2.8 Chapter 2 Assignment 2: Balancing Flash & Ambient for Dramatic Effects
- 2.9 Flash and Ambient Balancing For Creative Effect
- 2.10 Assignment: Balancing Flash & Ambient Light for Creative Effects
- 2.11 Understanding Flash Duration
- 2.12 Chapter 2 Quiz: The Basics of Flash
- 3.1 Chapter 3 Intro
- 3.2 5 Common Key Light Patterns 8M 45S
- 3.3 5 Common Key Light Patterns with Diffusion + Fill
- 3.4 5 Common Secondary Light Patterns
- 3.5 3 Primary Subject Positions
- 3.6 Assignment: Flat Light Portrait
- 3.7 Assignment: Loop Lighting
- 3.8 Assignment: Butterfly Lighting
- 3.9 Assignment: Rembrandt Portrait
- 3.10 Assignment: Split Lighting
- 3.11 Light Qualities 10M 3S
- 3.12 The Inverse Square Law 8M 20S
- 3.13 Inverse Square Law In Practice
- 3.14 Corrective White Balance
- 3.15 Creative White Balance 6M 4S
- 3.16 Assignment: Creative White Balance
- 3.17 Chapter 3 Quiz: Understanding Light
- 4.1 Chapter 4 Intro
- 4.2 On Board vs. Hot Shoe Flash
- 4.3 Full Feature vs. Manual Flashes 9M 6S
- 4.4 TTL vs. Manual Control
- 4.5 TTL vs. Manual Recycle Times
- 4.6 Flash Power & Zoom
- 4.7 HSS vs. ND Filters
- 4.8 Assignment: HSS vs. ND
- 4.9 FCS vs. RCS
- 4.10 Chapter 4 Quiz: On-Camera Flash Gear Basics
- 5.1 Chapter 5 Intro
- 5.2 4 Tips When You Must Use Direct Flash 6M 26S
- 5.3 Bare Bulbing Done Right
- 5.4 Assignment: Bare Bulb Flash Portrait
- 5.5 Grid Snoot + Direct Flash
- 5.6 Assignment: Grid/Snoot + Direct Flash Portrait
- 5.7 Mini Beauty + Direct Flash
- 5.8 Ring + Direct Flash
- 5.9 Assignment: Direct Flash with Modifier Portrait
- 5.10 Understanding Modifiers 9M 17S
- 5.11 Exercise: Understanding Modifiers
- 5.12 Direct Flash + Shutter Drags 9M 31S
- 5.13 Chapter 5 Assignment: Direct Flash + Shutter Drags
- 5.14 Chapter 5 Quiz: Direct Flash Done Right!
- 6.1 Ambient vs. Direct Flash vs. Bounce Flash
- 6.2 Chapter 6 Intro
- 6.3 Silver Bounce
- 6.4 More Light Silver + White
- 6.5 Assignment: Silver Bounce
- 6.6 Soft White Bounce
- 6.7 Assignment: Soft White Bounce
- 6.8 Overhead Bounce 11M 40S
- 6.9 Overhead Bounce + Fill
- 6.10 Assignment: Overhead Bounce
- 6.11 Event Bounce
- 6.12 Chapter 6 Quiz: Studio Light? Just Bounce It!
- 7.1 Chapter 7 Intro
- 7.2 Dramatic vs. Natural Light
- 7.3 Filling and Refining Existing Light
- 7.4 Multi-Point Light Setups 13M 52S
- 7.5 Assignment: Multi-Point Light Setups
- 7.6 Using Gels for Creative Effects vs. Corrective Effects
- 7.7 Assignment: Coloring Light for Creative Effect
- 7.8 Chapter 7 Quiz: More Lights, Refinement and Creativity
- 8.1 Chapter 8 Intro
- 8.2 Case Study 1 | Dramatic Sunset
- 8.3 Case Study 2 | Desert Sunset
- 8.4 Case Study 3 | Sinister Headshot
- 8.5 Case Study 4 | Quick Lighting for Family Portraits 8M 15S
- 8.6 Case Study 5 | Athlete Portraits
- 8.7 Case Study 6 | Working Angles
- 8.8 Case Study 7 | Drag + Composite
- 8.9 Case Study 8 | Less Is More
Total Course Run Time 8H 37M 51S
Tutorials Completed 0 / 66
Quizzes Completed 0 / 7
Assignment Completed 19 / 19