Color

Key Words

-Complemetary Colors of Light -Complementary Colors of Pigments -Dispersion -Pigment -Primary Colors -Secondary Color

Objectives

-Explain how a prism disperses white light into different colors -Analyze factors that determine the color of an object -Distinguish among primary, secondary, and complemetary colors of light and of pigments

The Colors of Objects

An object's color is the color of light that reaches your eye when you look at the object. The color of any object depends on what the object is made of and on the color of light that strikes the object. Sunlight contains all the colors of the visible spectrum. But when you look, for example, at a red car in sunlight, the red paint reflects mostly red light. Most of the other colors in white light are absorbed at the surface of the paint.

How does a prism separate white light into a visible spectrum?

As white light passes through a prism, shorter wavelengths refract more than longer wavelengths, and the colors separate. When red light, with its longer wavelength, enters a glass prism, it slows down the least of all the colors, and so is bent the least. Violet light is bent the most. The process in which white light separates into colors is called dispersion. A rainbow gives a beautiful example of dispersion. Droplets of water in the air act like prisms. They separate sunlight into the spectrum. When light enters a raindrop, it slows down and refracts. Then it reflects off the far inner surface of the raindrop. It refracts again as it exits the raindrop, speeds up, and travels back toward the source of light.

What color do you get when you mix the pigments of magenta and cyan?

Blue

When you mix any two colors of pigments, and they combine to make black, what is this known as?

Complementary colors of pigment

Mixing Colors of Light

Equal amounts of three colors of light--red, green, and blue--combine to prouce white light. Primary colors are three specific colors that can be combined in varying amounts to create all possible colors. The primary colors of light are red, green, and blue. When red light strikes a white surface, red light is reflected. Similarly, when blue light strikes a white surface, blue light is reflected. What happens if both red light and blue light strike a white surface? Both colors are reflected and the two colors add together to make a third color, magenta. When colors of light are mixed together, the colors add together to form a new color.

Separating White Light Into Colors

In 1666, the English physicist Isaac Newton investigated the visible spectrum. First, he used a glass prism to produce a visible spectrum from sunlight. With screens, he then blocked all colors of light except blue. Next, he placed a second prism where the blue light was visible. The second prism refracted the blue light but had no further effect on color. Newton's experiment showed that white sunlight is made up of all the colors of the visible spectrum.

What happens if you change the color of the light shining on an object?

Look at Figure 24, which shows the same stack of flower pots in several different colors of light. The pots appear to be different colors when viewed in different colors of light. For example, the red pot looks black when viewed in blue light because te red plastic absorbs all of the light striking it. No red light reaches the object, so none can be reflected from it.

Mixing Pigments

Paints, inks, photographs, and dyes get their colors from pigments. A pigment is a material that absorbs some colors of light and reflects other colors. Stone Age cave paintings were made with natural pigments from colored earth and clay. Over the centuries, natural pigments have been obtained from many sources, including metal oxide compounds, minerals, plants, and animals. Today's artists use paints made from natural pigments as well as from synthetic, or manufactured pigments. The primary colors of pigments are cyan, yellow, and magenta. You can mix varying amound of these primary pigment colors to make almost any other color. Each pigment reflects one or more colors. As pigments are mixed together, more colors are absorbed and fewer colors are reflected. When two or more pigments are mixed together, the colors absorbed by each pigment are subtracted out of the light that strikes the mixture. When cyan and magenta are combined, blue is formed. Cyan and yellow combine to form green. Yellow and magenta combine to form red. The secondary colors of pigments are red, green, and blue. Any two colors of pigments that combine to make black pigment are complementary colors of pigments.

Why does one see the primary pigment color yellow?

Primary pigment colors are a result of light waves that are reflected and interpreted by our eyes. We see yellow pigment because it absorbs blue light and reflects red and green light. When these red and green light waves overlap, our brain interprets the color yellow. The primary pigment colors are cyan, yellow, and magenta.

Secondary Color/Complementary Colors of Light

The secondary colors of light are cyan, yellow, and magenta. Each secondary color of light is a combination of two primary colors. Therefore, if you add a primary color to the proper secondary color, you will get white light. Any two colors of light that combine to form white light are complementary colors of light. A complementary color pair is a combination of one primary color and one secondary color. Blue and yellow are complementary colors of light, as are red and cyan, and green and magenta.

How do you make white light?

To get white light, you must combine two or more complementary colors of light, usually one primary color and one secondary color.

Why are different objects seen as different colors? For instance, why do we see grass as green?

We see objects as different colors because some light waves are absorbed while other are reflected. Grass is green because it absorbs red, orange, yellow, blue, indigo, and violet, but it reflects green. These green light waves are what our eye detects, and we see green grass.

What happens when you mix primary colors of light?

When you mix primary colors of light, which are red, green, and blue, you can see all of the other colors.