The rays are not coloured

Posted on Updated on

So when Newton wrote that the rays are not coloured, what exactly did he mean?

Well, he meant that even though we may say loosely that light at 400nm is blue and light at 700nm is red this implies that the blueness and the redness are properties of light.  Although there are philosophical arguments that would support colour as a property of light (and we’ll get on to those arguments in a later post) for now I would like to put forward my view (which is, I believe, consistent with Newton’s) that colour is not the property of light.

The evidence that supports my view is that light at 700nm may look red to most people most of the time, it doesn’t look red to all of the people most of the time or even to most of the people all of the time. For a very striking example please consider the image below:


In this example, you will see some blue spirals and some green spirals. But physically the blue and green are the same. In terms of wavelengths, exactly the same wavelengths (in exactly the same proportions) are being reflected from the areas that you perceive as being green and the those you perceive as being blue. If you think in terms of digital (RGB) terms, the RGB values of the green areas and the blue areas are the same – both are about R = 9, G = 20, B = 160. We know now that the colour that you perceive for a wavelength of light or a group of wavelengths depends upon the colours that are close by. This is often expressed as contrast or assimilation. When contrast occurs colours become less like the colours that they are next to an image; when assimilation occurs colours become more like the colours that they are next to. Contrast and assimilation effects result in you seeing two colours, a blue and a green, when physically only one colour exists.

Straight away some of you can see that I am falling into loose language straight away because I am using colour in two different ways. On the one hand I am saying the two colours are physically the same and on the other hand I am saying that the two colours are perceptually different (blue and green). Which is it? It all depends upon how you define colour. My stance is that I define colour as a perceptual phenomonon – it’s something we see and experience. Others may argue that the two colours are really the same and that it is a mere illusion that they look different – I, on the other hand, would argue that the two colours are different. It’s not an illusion – you see a blue and a green, don’t you?

This is what Newton was referring to when he said that “to speak properly, the rays are not coloured” – I believe that Newton was aware of this problem with language – that colour can be used to represent several things. But when we speak properly we realise that the rays are not coloured.


6 thoughts on “The rays are not coloured

    Reiner said:
    June 30, 2009 at 2:28 pm

    as much as I disagree with re-interpreting words after 300++ years of language change, I still would say that “ray => physics” and “colour => perception”
    “The limits of my language mean the limits of my world.”
    Wittgenstein 6.5

    swestland responded:
    June 30, 2009 at 5:37 pm

    I really must look into this chap called Wittenstein – lol

    Reiner said:
    June 30, 2009 at 7:57 pm

    meant to say: still agree that ray=physics

    swestland responded:
    July 1, 2009 at 8:19 am

    yes, I think we agree. The rays are physics and colour is perceptual. I think we agree.However, I have had several heated arguments with philosophers, many of whom belkieve that colour is the property oif light. I may make this the subject of the next blog 🙂

    Reiner said:
    July 1, 2009 at 1:00 pm

    You might just quote a different Philosopher:

    The sky is not blue.
    It merely looks that way,
    because blue is the name
    we have given that color.

    George Carlin

    The colour of the waves « my blog said:
    August 2, 2009 at 10:24 pm

    […] Stephen Westland has a very interesting article The Rays are not Coloured where he presents his observations of colour perception, how colours can be perceived differently […]

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s