Since elementary school, we all knew that there are 7 colors in the rainbow (from top to bottom): red, orange, yellow, green, blue, indigo and violet, which we all sung out or memorized using various mnemonics.
But have you ever wondered why there are only 7 colors in the rainbow, not more and not less? Additionally, the colors are usually seen in the same order day in and day out.
To understand this, we need to look at various aspects of colors.
The Visual Spectrum
You might have seen the visual spectrum but wasn’t even aware of it. This is because it is referred to as the visible light – and nearly everyone sees some form of light each day.
The visual spectrum is a narrow band of frequencies that are visible to the human light. The eyes see the light through the use of specialized cones and rods that are sensitive to the visual spectrum. Rods are sensitive to the presence or absence of light while cones are sensitive to colors. Cones come in three different types – blue, red and green.
Cone cells receive wavelengths that allow us to identify color, while rod cells receive low level light that allow you to see even in dim light. The cones activate depending on the color that you see. In some instances, a single cone might activate completely, with others activating partially. When you look at a white color, all the three cones become activated.
People who are colorblind are so because one or more of the cones don’t activate. So, how do they perceive the lights of the rainbow, you might ask? All they see is a smaller set of colors that aren’t prominent to them.
Color Perception by Humans
The human eye can sense wavelengths that range from deep red (700 nanometers) to violet (400 nanometers). The capacity to achieve this is due to the three types of photoreceptor proteins that the human eye contains, which produce a response due to stimuli.
Absence of Some Colors
Now that you know how your eyes perceive light, the next step is to understand why some colors are missing when you look at the rainbow. Seemingly you don’t see white, brown, pink, black and many other colors. Well, what we see in the rainbow are colors that are part of the spectrum.
The fact is that there are plenty of colors in the rainbow that we can’t see, but it doesn’t mean that they aren’t there. These colors are in the infrared and ultra-violet regions that our eyes can’t detect naturally.
What is more interesting is that every color of the rainbow comes from a single drop of rain. Red color is from high altitude drops while violet is from lower altitude drops. This means that millions of rain drops come together to form the rainbow. The size of the raindrops dictate the brightness of the rainbow.
Now you know a little more about the rainbow and what colors you need to expect from the colorful band in the sky!