What is Colour? Clearing up Chromatic Confusion.

Introduction

Perhaps one of the oldest philosophical questions goes something like this:

Why are objects the colour they are?

There are three main approaches to this.

  1. To treat colour as a property of the object being observed.
  2. Treat colour as a property of light.
  3. To treat colour as a mode of perception

In the 17th century, Isaac Newton performed a series of brilliant experiments on light. He shone white light through a prism and showed that you can separate it into rays of different coloured light. He took this to mean that colour is an intrinsic property of light.

When combined with his theory of light which treated light as a series of particles, this led him to believe there were different sizes of particles corresponding to different colours.

Blue is the result of particles of a certain size. Red is the result of particles of a different size and so forth.

So, Is Colour in The Light?

This has led many people to conclude that colour is a property intrinsic to light. As though light has a property of “blueness” or “redness”.

Many people still talk as though they believe that colour is a property of light. For instance, when people say something like:

Look at that light, it is blue light.

However, this is not the case. Light does not have a property of “blueness” or “redness” or any other colour. There is no property of light which corresponds directly to colour.

However, there is a property of light which causes the perception of certain colours, as we shall see in a moment.

So, there is no property of colour in light. You can study light all you want; you will not find this property. Suppose you could isolate a single photon and study every aspect of it.

You will never find a quality of “blueness” or “redness”. No matter how hard you look. Nobody ever has and you should not expect anyone to ever do so. So, what does that mean?

Photon
Mind you, modern physics does not have a clue what a photon is. Still, we can be sure it does not have the property “color”.
Creator: Illusterati
Available under a Attribution-Share Alike 3.0 Unported license.

Is Colour in the Object?

Prior to the idea that colour is in the light, it was widely believed that colour is “in the object” being perceived. It was believed that apples were red because of some kind of “redness” in the apples.

In other words, an apple appears red because it has some property of redness. The sky appears blue because it has some property of blueness. This view holds that if study the properties of things, you would find a “colour” property or attribute. Or, as though colour is “in the object”.

Many people still seem to think that colour is an attribute or property of an object. You can see this when they say things like:

That apple has a lot of redness in it.

But this is also wrong. Colour is not “in the object” nor is it “in the light”.

No matter how hard you look at apples, you will not find an attribute of “redness”. Nor will you find an attribute of “blueness” in the sky. Color is not in the object.

Colour is a form of perception which depends on the nature of the objects being observed. As well as the nature of the light interacting with the human eye.

Colour is a result of an interaction between the eye and the light being emitted or reflected from the object being observed.

As everyone knows, the eye reacts to light hitting the retina. Now, here is where it gets interesting…

As light behaves like a wave, it has a certain wavelength. The human eye can detect light of wavelengths between about 400 and about 900 nanometres (a nanometre is one-thousandth of a millionth of a metre). So, any light of wavelengths in this range is visible to the human eye.

Human eye
Of course, we are omitting a few details about how vision works. It is a complicated process. For our purposes we can ignore most of the details.

Light does come in other wavelengths outside of this spectrum. But the human eye can really only interact with light in that narrow range of wavelengths.

Of course, light of other wavelengths strikes the eye, however, the eye does not really interact with them in the context of human vision, so we do not need to worry about them.

Before we go any further, what is light? It is electromagnetic radiation.

What is that? It is, simply put, packets of energy that travel through space at “light speed” and which travel in a wave pattern. And since it travels as a wave, all electromagnetic radiation has a wavelength.

What is wavelength? We do not really need to get very technical on this. To put it simply, a wavelength is the distance between “peaks” of a wave.

What is important to grasp is that light comes in different wavelengths. Visible light comes in wavelengths between 400 and 900 nanometres. The electromagnetic waves in this range are the ones which are visible to the human eye.

As you might expect, not all visible light has the same wavelength. Some of it has a wavelength of closer to 400, some will be closer to 900 and some of it will fall in various values in between these.

For instance, light in the range of wavelengths of about 400-450 nanometres causes the perception of the colour violet. Light in the range of 450-485 nanometres causes the perception of the colour blue. And light in the range of 625-740 nanometres causes the perception of the colour red.

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