The smaller a light source is, the harder the light it produces and the greater the contrast between highlights and shadows. This is hard-edged lighting. Usually when using flash, the smallest we can make the source is to fire it bare without any modifiers. We also need to consider distance, as the further the light source is from the subject, the smaller it will be in relation to them. A good example of this is the sun. While it may be a huge mass of burning gas, the distance makes it a tiny spot in a large sky, which is why direct sunlight is very hard.