DIAGRAM 1-2. Surfaces and substances absorb some wavelengths while reflecting others. It is these reflected waves that create our perception of color.
talk about color, we are actually referring to wavelengths of light that produce a particular color. For example, when we talk about “blue light” we are really referring to the wavelengths that elicit the sensation of blue. We see the world in a multitude of colors because surfaces and substances absorb certain wavelengths and reflect other wavelengths back to our eyes.
The chart below is an overview of the energy (wavelengths measured in nanometers [nm]) and the color emitted.
LONGER WAVELENGTHS
Red . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .645nm
Yellow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .590nm
Green . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .540nm
Cyan (green-blue) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .500nm
SHORTER WAVELENGTHS
Blue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .455nm
Violet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .390nm
PRIMARY AND COMPLEMENTARY COLORS
Primary colors are a set of colors from which all other colors can be made. The primary colors for light (called the additive primaries) are red, green, and blue. The subtractive primary colors (usually used for pigments) are cyan, magenta, and yellow.
When all three subtractive colors are mixed together at full strength, the result is white (diagram 1-3; next page). When any two subtractive primaries are combined, the result is one of the additive primary colors. Conversely, when all three additive primary colors are mixed together at full strength, the result is black (diagram 1-4; page 15). When any two additive primaries are combined, the result is one of the subtractive primary colors.
HOW WE SEE COLOR VS. HOW THE CAMERA SEES COLOR
The Human Eye. The human eye contains two types of photoreceptor cells: rods and cones. These are located on the outer layer of the retina at the back of the eye. While the cones allow us to see different colors, the rods are used prima-
THE PHYSICS OF LIGHT 13
red
magenta yellow
blue |
cyan |
green |
rily for perceiving light and dark. For example, a person with fewer rods in his eyes may experience difficulty seeing in the dark. A person with abnormal cones in her eyes may experience partial color blindness, limiting his or her ability to differentiate between certain colors.
Furthermore, according to trichromatic theory, the human eye has three different types of cones: red, green, and blue. This enables us to perceive a multitude of colors. When cones that are sensitive to red are stimulated, we see red. When cones that are sensitive to green are stimulated, we see green. When red and green cones are equally stimulated, we see yellow—just as we can see in the subtractive primaries diagram (diagram 1-3).
Learned behavior is another factor in determining color. If you grew up with a certain cone deficiency and your parents continually told you a banana is yellow, you would be conditioned to say a banana is yellow. Similarly, in some cultures, classification of colors is limited to red, green, blue, and yellow; all variations of red, for example, are simply called “red.” In Western culture, on the other hand, we have an abundance of names for red and its many different shades and hues— “candy apple,” “scarlet,” and “crimson” to name just a few. It just goes to show that even cultural aspects have a lot to do with how we perceive colors.
Finally, it is important note that our eyes and brains also actively work to balance and neutralize colors, a phenomenon called chromatic adaptation. This is why a red apple always looks red, whether you are looking at it under a greenish fluorescent light or in the light of a pinkish sunset.
DIAGRAM 1-3. Combining all three subtractive primary colors in equal parts forms white. Combining any two creates one of the additive primary colors.
14 THE DIGITAL PHOTOGRAPHER’S GUIDE TO LIGHT MODIFIERS