Advanced Technique & Process 2A: Testing Inverse Square Law

3rd October 2014

My colleague and I worked together to test Inverse Square Law. We used a DSLR camera, a tripod, a light meter, natural light and a chair to create shots that tested whether the theory works.

Firstly we took a measure of the light and the aperture came out at f16, ISO 100, 1 sec. We took a shot. Then we doubled the distance of the subject from the light and took the same shot (with the same settings) to see if the light really had changed. We then applied the law which states that ‘double the distance, quarter the light’ so we went along 2 stops to f8. We shot again.
We found that in this instance there were many variables to the light in the area we shot the images. The sunlight from the window kept changing because of wind, which then blew the clouds swiftly over the sun and could not be defined as a definite, constant light source. We also (when moving double the distance away from the window – light source) found that the subject was closer to a tungsten light in the room and the white walls around the room reflected each of these light sources back towards the subject and around the room, which heavily affected the resulting image.
As a result of this we tried the same image at f9 instead and this definitely was an improvement.

We found that the law didn’t work fully in most situations, depending on the unique qualities within each area we shot. We witnessed different light sources, reflections of light bounced off of shiny surfaces and painted walls/floors, different textures, and in one instance a door frame that blocked light in some areas but not others.

To conclude, the Inverse Square Law only works in ‘perfect’ lighting conditions – e.g in a studio setting, where light can be controlled.

Window Light:

IW9B0225RESIZED f16

IW9B0226RESIZED IW9B0228RESIZED
^ f16 (distanced doubled), ^ f8 (distance doubled)

IW9B0229RESIZED f9 (distance doubled)

Tall Window Light Source

IW9B0231RESIZED f16

IW9B0233RESIZED IW9B0235RESIZED
^ f16 (distance doubled),  ^ f8 (distance doubled)

IW9B0236RESIZED f11 (distance doubled)

Stairs (dim yet spotted window light)

IW9B0244RESIZED f4

IW9B0245RESIZED IW9B0246RESIZED

^ f4 (distanced doubled),   ^ f2.8 (distanced doubled)

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