Inverse Square Law; Double the distance = quarter the light
I experimented this theory within the studio with 3 different set ups of light. In each set up i measured a distance of 5FT from the light source. I then metered a whole number aperture on 100 ISO. Once we had the distance and Aperture worked out we doubled the distance (1/4 the light ) therefore we must move 2 Fstops. Overall i have discovered that Inverse Square Law generally works, however it can be wrong under some light circumstances. I found that different factors affect the outcome such as; angle of light, reflection of light, distances of light and subject as this can change drastically with the slightest of movements.
In the first experiment i found the Law worked. The light was pointing down at the floor which meant the light carried out.I measured at 5FT, 100 ISO, F11, exposure of 1 sec. I then doubled the distance and 1/4 the light (moved 2 stops) to F5.6, exposure of 4 seconds.
In the second experiment i found that the Law didn’t work.The light was from a soft box angled at a white surface. I measured at 5Ft, 100 ISO, F11, exposure of 1 sec. I then doubled the distance which should have 1/4 the light to F5.6 however the measured light measured 3 F-stops not 2 making it F4. I found the factors of the angle of the soft box spread the light out in a larger distance and did not carry it fully across the backdrop. Also as the light was reflecting off the white surface the light source was also lower. These factors weight up the different outcome.
In the third experiment i also found that the Law didn’t work. The light was a flood light spread across a black wall. I measured at 5Ft, 100 ISO, F32, 1 Sec exposure.I then doubled the distance and 1/4 the light and reached F16, (this proved the law worked) however i then doubled the distance again which meant i 1/8 the light and reached F11, (i should have reached F8 – therefore law doesn’t work properly) i then doubled the distance again, 1/16 the light and reached F8. Therefore this proved that the Law doesn’t always work. However i do believe that factors of the experiment may have also affected this, the light was at a slight angle against the wall and the light was being absorbed by the black wall.
After these experiments i now feel i understand Inverse Square Law and accept that it isn’t always 100% accurate. However i do feel i should be able to apply this to my work now.
Below are a few quick snaps of the experiments i worked on…