Project 38 - measuring the intensity of light

For this project, I used ISO 100 on my digital camera and a fixed shutter speed of 1/125 secs. I was blessed with a warm, sunny October day here in Spain.

Sunrise was at 08.25 and I took my first reading at 08.55. Sunset was at 20.25 and the last reading was taken at 19.00. The results were as follows-

o8.55 - f/3.5
09.30 - f/11
10.00 - f/14
10.30 - f/13 (slight haze)
11.00 - f/16
11.30 - f/16
12.30 - f/16
13.30 - f/16
14.00 - f/16
15.00 - f/16
16.00 - f/16
17.00 - f/13 (slight haze)
18.00 - f/13
19.00 - f/11

As predicted in the course notes, the readings levelled off later in the morning as the sun reached about 40 degrees.

In other seasons, I would expect the width of the 'maximum brightness' band to increase as the sun would be above 40 degrees for longest in mid-summer (more time at the maximum) and for the shortest time in mid-winter (less time at the maximum).

Before this section on lighting, I would have thought that the intensity of light would increase during the day to a peak and that the intensity would be greatest at the Equator, where the sun is directly overhead, than in the UK (say). This does not appear to be the case.

Finally, a couple of readings were taken indoors during the day. Whilst the required f-stop outside was 16, that indoors varied from 5.6 to 9, about 2 to 3 f-stops lower, showing that there are lower light levels indoors even on a bright, sunny day.