Advanced Technique & Process 2A: Inverse Square Law

26th Sept 2014

The Inverse Square Law states that if you double the distance away from the light source, you are quartering the light, therefore that would mean adjusting 2 stops.

In class we were taught about the Inverse Square Law, then had to put it to the test. We had a number of different light set ups in the studio and we used our DSLR cameras, a light meter, a tape measure and we worked in pairs. The findings were interesting because even in what would be considered ‘perfect’ lighting conditions their were still variables that swayed the theory.

We set the ISO to 100 and the shutter speed to 1 sec and only adjusted the aperture to test the law.

Set up 1

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The first set up my colleague and I tested was a light positioned close to the ground, with the light running across the floor, bouncing back upwards & off of the white panel positioned next to the light source. We measured the light running across the floor from the light source to 12ft away. There was a definite inconsistency with the way the light travelled for this particular set up. We figured out that the pattern and colour of the floor had an important role to play in this. It was grey and patterned, so the light wont have travelled along it as smoothly as a clear floor. Darker colours absorb the light more too. The light that bounced off from the side board will have also affected the readings.

1ft: f32/45
6ft: f11
12ft: f5.6

Set up 2
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The second set up was a light angled down at the floor slightly but carrying along the white back ground. We measured from the light itself to the ground, then onwards along the floor. Again there was a slight inconsistency with the readings, because of the reflected light and the shape of the back drop.

1ft: f22
5ft: f11.5, but
6ft: f11, then
10ft: f5.6 3/4 so = f8

Set up 3

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For this set up there was just one large light source pointing towards and bouncing off of the wall. As you can see on the image the fade off happens quite suddenly after the light hits the wall. This is because the wall is black and therefore absorbs the light better. This also left slight inconsistencies within the readings, although they were reasonably accurate for this light source set up.

5ft: f32
10ft: f16 (almost f22)
15ft: f11
20ft: f8

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