..Even though you are learning about this last, this is the most important element, which makes photography even possible. Since you are composing using light, it is fundamental to understand all the different aspects of controlling light. Light in photography can come from many sources or just a single source. The sources all produce light that has certain qualities, which can change the way your image look dramatically.

Intensity - The value of the light is measured in it's intensity. How bright or dim the light you work with is how you decide your f-stop and shutter speed.

Degree of Diffusion - Light can be well distributed, or it can be very focused. Sharp or focused light usually cause very hard shadows, with little contrast. It usually originates from a flash or the sun in a cloudless sky. On the other hand, light can be diffused. Such light can be found outside on a cloudy day, or in a gym with multiple lights above. Diffused light causes hazy, ill-defined, poor shadows, or even non at all.

Direction - The angle at which light stikes your subject is called the direction. It can affect shadows, textures, and appearence of your subject. Sidelight which strikes your subject directly form the side can often emphasize textures or a surface. Frontlight usually minimizes texture and shadows on your subject. Backlight, usually casts a dark shadow(s) on the subject, but can illuminate the subject, creating a light haze around it. Bottom lighting is from a light source below the subject. It is often unatural or sinister looking.

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