What is light?
Light is really energy that travels in waves. Light waves consist of both magnetic and electric fields of energy. These are known as electromagnetic fields. The visible part is only a small section of the full range of the electromagnetic spectrum. Other sections include radio, microwaves, infrared, ultraviolet, X-rays and gamma rays. Each type is differentiated by their unique wavelengths.
Our concern as photographers is with the visible spectrum. Light can be natural or artificial. The way we use it plays a significant role in the impact of our pictures. Flash can be used in conjunction with available and artificial light. It can be dramatic or soft depending on what or who you are photographing. A baby for example is better photographed with soft light. Where as a rock star or a model can be photographed in a more dramatic way.
Light therefore is what creates our image - how it is seen and how it is interpreted. A photograph can have luminance with the proper exposure and all is fine. But it will have a greater impact if there is lighting, the kind that you can see which draws you in and around the picture.
How light behaves
The way light behaves is very predictable. It can be reflected, transmitted, absorbed or refracted. Light is reflected when it is bounced off a surface. It comes off at the same angle as it was received. There is a law stating this effect and it reads as follows: 'the angle of incidence equals the angle of reflection'. In other words the light will reflect off a flat surface in the same angle as it was received. The main concern is the type of surface it is reflected from and the color of the surface.
When using reflectors, for example, the effect the light will have on the subject will depend on what material was used and the color of that material. If you use a smooth silver colored reflector its effect will be harsh. A gold reflector will produce a warmer color although still harsh due to the texture of the surface. Most reflectors are made of a slightly rough uneven material. When light is bounced off them it becomes dispersed and soft. The causes a more pleasing and flattering look.
Umbrellas are also reflective. Light is directed into them and scattered back to the subject. There are silver, white and gold colored umbrellas. Some have a smooth surface while others are rough and uneven. Some white umbrellas allow for light to be passed through them almost like a soft-box. Because of their design, the light that is produced is broad and mostly diffused. The ones with a smoother shinier surface tend to be less diffused. Walls and ceilings are another good medium for reflecting light especially flash. A small twist of an on-camera flash towards a wall can make all the difference.
Transmitted light passes through a medium. It can be a fabric of translucent material, glass, or plastic. A soft-box is one example where the light passes through material to create a light that is soft and diffused but not as broad as umbrella lighting. Soft boxes are more directional yet soft enough not to cause unwanted harshness.
Another type of medium that light passes through are spots and Fresnel lenses mostly used in theater. Fresnel lenses are not necessarily used for photography but they are mentioned here in order to help understand how refraction. The light source is placed close to the lens. It is gathered and focused into a condensed beam which allows for use over greater distances.
The absorption of light is when a dark material is used, such as a black velvet cloth. Black material is used to produce the opposite effect of a reflector which bounces reflected light into the picture. It therefore subtracts rather than adds.
Light is predictable and manageable. Great photographs are created by those who consciously look for the light and understand the impact it has in our images.