Light is the essence of photography. Without light there is no photography. Light is the photographer’s  medium. The word photography is derived from the ancient Greek words, ‘photos’ and ‘graph’, meaning ‘light writing’. To understand light the photographer must be fully conversant with its qualities and behaviour. In mastering the medium the photographer learns to take control over the creation of the fi nal image. This takes knowledge, skill and craftsmanship. It can at fi rst seem
complex and sometimes confusing. However, with increased awareness and ractical experience light becomes an invaluable tool to communication.

Seeing light 

In order to manage a light source, we must fi rst be aware of its presence. Often our preoccupation with content and framing can make us oblivious to the light alling on the subject and background. We naturally take light for granted. This can ometimes cause us to simply forget to ‘see’ the light.
When light falls on a subject it creates a range of tones we can group into three main categories:
Highlights, Mid-tones and Shadows.
Each of these can be described by their level of illumination (how bright, how dark) and their distribution within the frame. These are in turn dictated by the relative position of Subject, Light source and Camera.

Introducing light
The major difference between studio and location photography is the studio itself has no ambient or inherent light. The photographer starts with no light at all and has to previsualise how to light the subject matter and what effect that light will have upon the subject. Studio photographers have to conceive the lighting of the subject rather than observe what already exists. This requires knowledge, craft, observation, organisation and discipline. Good studio photography takes time,
lots of time, and patience.

Understanding the nature of light
In order to make the best use of an artifi cial light source, we must fi rst be aware of how light acts and reacts in nature. Observation of direct sunlight, diffuse sunlight through cloud and all its many variations will develop an understanding of the two main artifi cial studio light sources available. A spotlight (point light source) imitates the type of light we see from direct sunlight, a hard light with strong shadows and extreme contrast. A fl oodlight (diffuse light source) imitates the type of light we see on an overcast day, a soft diffuse light with minor variations in contrast and few shadows.
To understand light fully it is essential to examine its individual characteristics.
~ Source
~ Intensity
~ Quality
~ Colour
~ Direction
~ Contrast.

[the above material is from Photographic Lighting (3rd)]