We are capable of perceiving only a fraction of the electromagnetic spectrum. A quantitative analysis of the different wavelengths at which visible colors are perceived, is presented in this article.
Visible Color Spectrum Wheel
The visible color spectrum wheel is an arrangement of colors in a wheel or circle to show how one color relates to the other.
All of us are familiar with the color wheel, which we have seen in a painting class, or while studying about light wavelength in physics. This wheel is nothing but a visual chart of all visible colors that are arranged in a certain way. This is done so that we can understand the relationship between colors, and which ones are complimentary or contrasting. This is useful in interior decoration, garment designing, and other related fields where harmony of colors is vital. The first color wheel was invented by Sir Isaac Newton in 1706, when he passed a beam of sunlight through a prism, and it produced the colors of the visible spectrum.
So, the next question is: what is the visible spectrum? Light, as we all know, is an electromagnetic wave, which is visible to our eyes. There are other electromagnetic waves such as radio waves, ultraviolet waves, infra-rays, and microwaves, which are not visible to the human eye. Each color that we actually see, has a different wavelength, and that is why, we are able to discern them as different colors. Sunlight or white light is composed of these different wavelengths of light, and we can see them as different colors, when it is passed through a prism. This is known as the wavelength of visible light spectrum.
When a ray of light falls on a colored object, most of the light is absorbed and only one color is reflected. For example, a blue object absorbs nearly the full spectrum of light, reflecting the color blue only. Thus, when we see blue, or for that matter, any colored object, it means that the respective color is only reflected, and all the other ones are absorbed.
Arrangement of Colors
The wavelength of visible light is between 390 to 750 nm, which is visible to the naked eye in the form of light. In a standard color wheel, all the visible colors are painted on a circle. The three primaries (red, yellow, and blue) are placed around the three points of an equilateral triangle; they are also known as pure colors, as they cannot be made by mixing any other colors.
The secondaries (green, orange, and violet) are then placed in between the primaries at equal distances. They are made by mixing two primary colors in equal proportions. Orange is made by mixing red with yellow; violet is made by mixing red with blue; and green is made by mixing blue with yellow. The six tertiary colors, which are red-orange, red-violet, yellow-green, yellow-orange, blue-green, and blue-violet, are made by mixing each primary color with the adjacent secondary one.
For example, red-orange is made by mixing red (primary) with orange (secondary). Red orange is then placed in between red and orange in the wheel. All the other five tertiary types are placed in it in the same way, i.e., in between the primaries and the secondaries from which they are made.
These 12 colors form the basis of this wheel. However, in reality, there are many more varieties, shades, and hues. Many such wheels show more gradation of colors and have 24 colors on them. In theory, all of them can be made by mixing the primary, with the secondary and tertiary ones; and the total number will be infinite. But in reality, it is very difficult for paint companies to come up with so many variations.
One of the most interesting facts about this wheel is that if it is spinning rapidly, our eyes can see the color white, which is not even there in it. When it spins rapidly, the colors merge into each other very fast, and our mind is not able to distinguish between them. So, their reflection is blended, and we see white light. When all the light of the visible spectrum is absorbed, we see the color black. The color wheel is thus, invaluable for artists as well as physicists, who study the interaction of colors.