Sometimes you can’t wait for the perfect light, and the only option is to modify the existing light. There are two excellent tools which every photographer may use to modify light: diffusers and reflectors. » Read more: Accessories to Control Light

Supplemental Light
Supplemental light is the light which you bring to the scene. Using supplemental light may give you an amazing control over the photographs. When using supplemental light, you can control the color, direction, intensity, and diffusion of the light. The two main examples of supplemental light are the small dedicated flash units and studio lights. » Read more: Photography and light

Red eye is a phenomenon that has affected every photographer at some time or another. It is the glowing red eyes caused when the light from a flash is reflected off the blood vessels in your subjects’ retina. Red eye may ruin even the best photo. The closer the flash is to the lens, the more likely there will be red eye (which is why red eye is a very common problem on point and shoot cameras). As the distance between the flash and the lens increases, the chance of red eye decreases. » Read more: Red eye and Red-eye reduction

Available Light
Available light is any light that exists in the scene naturally. This can be the sun in the sky or a neon sign. Just think of it as light that is already there, that you are not likely to be able to do anything to change. » Read more: Light types

When the light rays are scattered by being reflected or by passing through a translucent material that light is diffused. Diffused light provides a more even light and softens shadows in your photograph. You can diffuse artificial light using utensils such as reflectors, diffusers, umbrellas, and softboxes. You can also use diffusers and reflectors to help soften natural light. However, for natural light, the best diffuser is a strong cloud cover, which lessens the intensity of the sunlight as it reaches your subject. » Read more: The Diffusion of Light