Advanced Technique & Process 2A: Testing Inverse Square Law (pt 3) – Day light

29th October 2014

Here I went around on location in Bradford looking for spots where I could test the inverse square law. I used daylight and looked for a variety of spots where the light was different. I aimed to test the law and see if it could be proven correct/incorrect. The only problem here was that a lot of it was guess work – I didn’t use a light meter (except for the one in-camera) and I didn’t use a tape measure, but just guesstimated the distance. Here are my results…



1/125 sec, f11, ISO 100. Same again (distance doubled). 1/125 sec, f5.6, ISO 100.

Here I wanted to see if when moving away from direct sunlight, the lighting changed or stayed the same. The thing is, the sun is a vast light source – it lights up the planet! So it’s hard to ‘get away from it’ or for it to ‘dim’ in an open public place. However I tested it on a slight hill where there were some trees (which also would interfere with the law!) that cast shadows on the wall behind. The law has worked here to a degree, because the subjects face has been exposed correctly on the last image, however it isn’t a ‘perfect’ lighting scenario. The first image is exposed correctly, however the end image is over exposed and bleached out white.

Opening of a walkway tunnel:


1/50 sec, f8, ISO 1600. Same again (distance doubled). 1/50 sec, f4, ISO 1600.

Here I think I have a more accurate exposure after testing the law by doubling the distance and quartering the light. The reason for this is I believe because it was pure daylight and there were no other interferences from other light sources or e.g shadows cast. I think the error with this test in particular was that I didn’t double the distance exactly (because I didn’t use a tape measure). Maybe I should have moved even further into the tunnel, to get a more accurate image as the end product, because it is just slightly over exposed.

Walkway tunnel (with tungsten light above in part):


1/25 sec, f8, ISO 3200. Same but at f4, distance doubled.

This location was quite interesting because when you looked down the tunnel, you could see how the natural light faded the further you entered into it. However this is why they have tungsten lighting in this tunnel, so that it’s not completely dark when walking through e.g at night. Then, this leads to another issue for the inverse square law – some of the lights in the tunnel don’t work. For example you could have 4 along the top of one wall and 2 of them work. So this interfered with my test – because I tried to go for the wall where there was the least tungsten light. However the positioning of the lights that worked, didn’t work to my advantage. As you can see here the first image is closer to the entrance of the tunnel and has more daylight coming in from the left hand side of the subject, but the second image (distance doubled) taken further into the tunnel is slightly blown out and is lit with tungsten light.

Curved wall:


1/50, f8, ISO 1600. Same settings with the distance doubled. Then at f4.

This was an interesting set up. It was a curved wall in The Impressions Gallery, with the light coming in from the left side of the subject, but also as you moved along the wall there was a window opposite the subject that light travelled through but was diffused light because of a semi-transparent poster on the window. I would say the law has worked rather well here, however without the help of the window opposite the subject on the second and third image, it may not have worked as well. One thing I’ve noticed in testing the inverse square law is that the light may be correctly exposed on both images, but the way the light hits the subject and ‘fills the image’ – is different. This may just be because of the locations I’ve chosen to shoot in, but I will look into this further.

Large Window:


1/25 sec, f11, ISO 800. Distance doubled, so at f5.6.

IW9B4238-02RESIZED < the subject between the two points (to show the surrounding area)
1/160 sec, f5.6, ISO 800.

I noticed here that the exposure, just capturing the subject close up (image 1), was lighter than the exposure for the whole wall and the subject (image 3). I think this was because when photographing closer I am primarily considering the exposure of the person – their clothes etc, but when photographing wider I, and the camera are considering the exposure of the whole surroundings.

Cathedral steps with natural day light only:


1/32 sec, f8, ISO 3200. Same with distance doubled. Then at f4.

For me this location came out with the most successful results of the day.


1/32 sec, f8, ISO 3200. Same but the subject is double the distance away from the light. then at f4.

^ Here we can see that on the third image, the inverse square law has worked for the subject, however the background is blown out. This shows that the law works though in this case, shown with these closer images…


1/50 sec, f8, ISO 6400. Same, distance doubled. Then at f4.

The closer to the ‘light source’ the more dramatic the light on the subject is. The further away the subject from the light source, the softer the light is, and the more it seems to ‘spread out’. In the example above this is very evident from the first image to the third.

To conclude this shoot I would say that there is definitely an irregularity between each test, because of many factors. Two of the major factors would be that I had no light meter and no tape measure!! Therefore some of my exposures haven’t even turned out right on the first image, never mind the ones that follow. Also, each light source varies completely. There are differences in lighting between each location, especially when in a public place. I would say that the Cathedral steps were the most successful in proving that the law works, because there was no other interference with the light. Next, I might try this again and use a tape measure and light meter to obtain an accuracy within my testing, to see if I can find a scenario where the law works.

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