This exercise is to experiment with a simple technique, concentrating light. Sometimes, I may want the light to fall on just a part of the scene having the surrounds in shadow, as it explains in the exercise wording. Unfortunately I am unable to put this into practice as I do not own a flash. The exercise advises against experimenting with tungsten lamps due to the heat output. However, I do understand the concept. Once I own a flash unit I will experiment with this technique.
For example, I could use a piece of dark rolled up card attached to my flash to concentrate the light, all other light in the room would be minimal, illuminating the subject. I could even use objects which can be found around the house. A pringles tube for example, wrapping paper tube or even a toilet paper tube. It will be interesting to see how the length and circumference of the tube can effect the end result. I could also experiment with using a diffuser on the end of the tube and see how this will effect the image.
See the images below which I have collected from the internet, demonstrating concentrated light.
The images above and below, show that even the most simple of techniques (such as concentrating a light source) can have very dramatic and striking results.