Imaginary Colors

I was watching QI (a BBC program of semi-serious questions and semi-serious answers, QI = Quite Interesting) and one of the questions which came up a few weeks ago was about imaginary colors. They messed up the graphics quite badly like this:


So colors between deep blue and purple-red are not supposed to exist. QI did not explain why. I've seen in some textbooks that these colors are described as mysterious or anomolous. In the textbooks  this diagram is used...



...which at least gives a bit more "explanation" of why they should not be visible. According to some people, since they are on that strange lower edge, and not on the "spectral edge" they are therefore non-existent colors.

(I found the reasoning to have the same weight as those who say "science says bumble bees should not be able to fly, but they can, so science is wrong!" It is clear to anyone with half a brain that bumble bees are not shaped like aircraft, are lighter and less dense. The science which explains bumble bee flight is going to be different to the science which explains the flight of huge passenger jets.) 

Back to colors though. There's two things wrong with this "science says we can't see mysterious colors but we can!" "reasoning":
  1. We can see colors which are not on the spectral edge, white is a good example. In other words we can see colors which are inside the shape shown above. Light yellow is another good example. So how near to the mysterious edge does a color need to be for it to become become mysterious? Clearly an arbitrary distance.
  2. We see colors because our eyes/brain (during daylight) mixes singals from three sensors (red green and blue). Our eyes don't even "know" about that mysterious edge. The diagram above is useful but it is not what goes on in the brain.



Comments

  1. AnonymousMay 4, 2022 at 5:09 AM

    Hello, I am a physics teacher with specific experience in working in the visual and infrared optics.

    In quantum mechanics, we define a quanta as a discrete packet of energy. Light can be described as quanta, with specific wavelengths that define the energy that this light transfers from the source to your eyes. These wavelengths are given on the second diagram (the blue numbers around the black curve - known as the spectral colours). All of the colours on this black curve have specific wavelengths and thus a definitive energy. This energy has a corresponding colour (dependent on the calibration of our eyes and brain). But where is pink? notice it is not on this spectral line. In fact, all of the colours inside this spectral line are also not on this line - they are imaginary.

    But why imaginary, why not real.... the simple answer being that we see these colours as a result of multiple real colours (those that are on the spectral line) reaching our optical system (eyes and brain) at the same time.

    Pink is the simplest example. If my cup is pink it is so because it absorbs most of the light on the spectral line..... except for violet and red. These two discrete spectral quanta reflect off of the cup and into my eyes. However, instead of seeing violet and red individually my optical system has developed to produce something completely new, completely imaginary... pink.

    Picking a point on the graph (0.3, 0.2) is a pale pink colour. Why is it paler? Well, it is because there are now more quanta, of varying energies entering the eyes. This is picked up by the rods in the retina, responsible for detecting level of brightness. The more energy on these rods, the brighter the image becomes and the paler the colour becomes.

    I hope this helps.

    ReplyDelete
  2. AnonymousMay 4, 2022 at 5:13 AM

    Please bare in mind. I am using "imaginary" in my own definition to say that these colours are developed by the brain. Some sources may call these "additive colours" and define them as real, because they are detectable by the human eye.

    However, these additive colours are not a results of one, specific, discrete quanta of energy - hence the term "additive".

    ReplyDelete

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