Lighting / Learn by doing
Inverse-square Law explained simply
What is โInverse-square Lawโ?
For an ideal point source, illumination falls with the square of distance. Doubling distance gives roughly one-quarter of the light.
- 011ร distance
- 022ร distance
- 03About 1/4 illumination
How do you use Inverse-square Law practically?
A small exercise
Use a small light at one metre and then two metres from a still subject. Compare readings, allowing for your real modifier and room reflections.
- Make a starting version and keep it so you can compare fairly.
- Try the change in the exercise. Keep unrelated choices steady where the exercise allows.
- Compare the result at the size your viewer will actually see. Write down what changed and whether it helped.
How does Inverse-square Law solve a problem?
It helps plan exposure changes and understand why a nearby light can make a background much darker.
What can go wrong?
Large nearby sources, focused beams and room bounce do not behave exactly like an ideal point source.
How do you turn the idea into a useful solution?
Start with the specific problem in your image or brief, try the exercise, and keep the version that meets that need. If the result is worse, return to the starting version and change one choice at a time.
Quick check: can you explain the three ideas in the diagram?
1ร distance โ 2ร distance โ About 1/4 illumination. Explain how each relates to the exercise. Then compare the starting version with your result and choose the one that meets your brief.
Related video lesson
Portrait lighting โ Adorama
This related lesson gives wider context for the topic. Camera menus and software versions may differ from yours.
Loading the player connects to YouTube. You can also watch the lesson on YouTube.Keep exploring
Try the idea in a studio shoot
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