There are 4 types of lighting qualities. Today we will explore the differences and how to use each of them.
1) Hard Light
A typical example of hard light is when sunlight hits without any cloud. Hard light will exaggerate wrinkles, blemishes and pretty much at uneven surfaces on your subject. Image shot with hard light will have high contrast and well defined lines between highlight and shadow.
The rule of getting hard light is that the smaller the source of light, and the further the source of light relative to your subject, the harder the light source.
2) Soft Light
When there's cloud hovering between sunlight and subject, you will get a soft light because the source of light has increased it's surface area. In contrast with hard light, soft light will hide wrinkles, blemishes and any uneven surfaces on your subject. Image shot with soft light will have low contrast and gradually defined lines between highlight and shadow.
The rule of getting soft light is that the larger the source of light, and the closer the source of light relative to your subject, the softer the light source.
3) Diffuse Light
Diffuse light is produced when there is a diffuser in front your light source, such as a white sheet of diffuser panel in front of your softbox, or cloud in the sky. However, you may use something like magmod sphere to diffuse hard light, to produce a hard but diffused light. Diffused light is when you don't see much details on on your subject, such as sweat. For example, when hard light (from a small light source) is diffused, you still get the hard defined shadows, but the light reflected from your subject has less 'shiny' effect. To achieve maximum soft light, you may use a large softbox together with a diffuser, you will get a combination of soft shadow and hide any sweat or pore spots effectively. Diffuse light can also be produced when you reflect light from a soft white reflector.
4) Specular Light
In contrast with soft light, specular light with give you a shiny look on sweat and pores, or if your subject has oily face, you will see super bright oily forehead. Specular light can be produced when you remove the inner lining and diffuser panel from your softbox, leaving the shining walls exposed directly to the light and your subject. You can still achieve soft quality light, with a punch of sharpness by using this method. This specular light application is usually used for shooting a punchy feel type of photo. Specular light can also be produced when you reflect light with a shiny reflector.
To summarize: Soft light is when the light source is big and near to your subject.
Hard light is when the light source is small and far away from your subject.
Diffuse light is produced when you have a diffuser in front of light, or when light is reflected from a soft white reflector.
Specular light is when there is no diffuser, or when light is reflected from silver/shiny reflector.