The apparent size of a light source depends on its relative size to the subject and its distance from the subject. The relative size of a light source has a dramatic effect on the shape and brightness of the highlight as well as the softness of shadows cast by the light.
A light source that is relatively large compared to a subject (a large softbox 3 feet from an apple, for example) will result in soft shadows, low contrast and a less sharp highlight. A smaller light source (small bulb 3 feet from the same apple) will result in greater contrast, increased brightness in the highlight and sharper shadows. Typically, portrait photographers desire a large relative light source for its soft qualities.
Distance from the subject can also cause the same light source to appear soft or harsh. A large softbox is relatively larger than an apple at 3 feet, but moving the softbox back to 15 feet makes it much smaller relative to the apple thus producing the same hard light that would come from a small source that was close to the apple. This is the reason for the various sizes of light modifiers that are available.
Experiment with your light source to see the effects of relative size and distance to subject. Soon you will be able to predict the results of your lighting setup when you make changes. A smooth object like a ball will most easily show the light quality in your photo.