1. THE PHYSICS OF LIGHT

Have you ever noticed that the colors in color photographs don’t appear the same way we originally saw them? Of course you have. It’s because the range of brightness and shades of color seen by the human eye are quite different

than those recorded in a photograph.

What the human eye sees is not what will be recorded on film or on a digital sensor. The human eye adapts and adjusts to the color, saturation, and brightness or darkness of its environment. Film and digital sensors, on the other hand, do not; they record the actual colors and illumination rendered from the light source. For example, a camera records indoor tungsten light as yellow/orange, while the human eye sees it as a form of white. Understanding this phenomenon is key to producing images of the highest color and image quality.

PERCEPTION OF LIGHT AS COLOR

Visible light, the part of the electromagnetic spectrum that can be seen by the human eye, forms tiny bands of wavelengths among many other forms of radiant energy. The human body can detect shorter wavelengths, such as x-ray and ultraviolet light, because they penetrate tissue; longer wavelengths, such as infrared and microwaves, have no direct effect because the energy emitted is so low.

It is only at wavelengths between 400nm and 700nm that the human eye registers what is perceived as light. Within this visible range, Isaac Newton proved that stimuli of different wavelengths produce all of the different colors. When we

yellow

narrow slit

green

blue shorter wavelengths

DIAGRAM 1-1. When light emitted from a white-light source passes through a narrow slit and a prism, it separates into component wavelengths of different colors.

12 THE DIGITAL PHOTOGRAPHER’S GUIDE TO LIGHT MODIFIERS