Why do most rainbows look stripy?

[MiM]

In another thread JimC said

"Of course, there are situations where humans do grab discreteness where none really exists; the classic example would be the names we give to the colours of the rainbow; quantum effects aside, the spectrum of light is a true continuum, and our "chunking" of it is a process of our consciousness. The fact that the human mind does this (for quite practical reasons) in some circumstances is not evidence that the whole of reality is non-discrete."

Obviously he is right about the spectrum of colours being a (de facto) continuum. But then why does the average rainbow you see in the sky most often look like if it had, not clear cut, but still distinctive stripes of different colour that blend into each other in narrow regions. Is this an effect of the physics of the rainbow, the physiology of the eye, or is it something we have learned to see?

[JacksSmirkingRevenge]

[JimC]

If you do a graph of the intensity of sunlight vs wavelength, it's not a horizontal line, it has some mild ups and downs. However, it doesn't come as a series of peaks, corresponding to colours we name. Basically, I think the stripy effect is most likely psychological, and part of a process of "chunking" because that makes it easier to describe and name.

[klr]

This has also occupied some waking minutes of mine as well. That and the pot o' gold ...

If you do a graph of the intensity of sunlight vs wavelength, it's not a horizontal line, it has some mild ups and downs. However, it doesn't come as a series of peaks, corresponding to colours we name. Basically, I think the stripy effect is most likely psychological, and part of a process of "chunking" because that makes it easier to describe and name.

EDIT: Yes, I said WA-KING

[JacksSmirkingRevenge]

If you do a graph of the intensity of sunlight vs wavelength, it's not a horizontal line, it has some mild ups and downs. However, it doesn't come as a series of peaks, corresponding to colours we name. Basically, I think the stripy effect is most likely psychological, and part of a process of "chunking" because that makes it easier to describe and name.

I don't know if the phenomena are related, but something similar seems true of sound volume...
The volume potentiometers on electric guitars are linear ones and the volume seems to jump quite dramatically when turned up. That is, it sounds non-linear.
The volume potentiometers on equipment like a cd player (for example) are made logarithmic in order to make them sound linear and allow for more precise control.

Somebody correct me if I'm wrong here. It's been some time since I read about this stuff.

[macdoc]

I suspect just from the physics it's the color receptors in your eyes - humans ( most not all ) have tricolour vision. There will be primary and then complimentary colours the eye reacts to.

But it's just a guess.

[Xamonas Chegwé]

I think Macdoc has nailed it. We don't see the full spectrum of colours equally well due to only actually sensing three separate wavelengths..

[subversive science]

The discrete nature of rainbows is a consequence of neural image processing.

[JimC]

The discrete nature of rainbows is a consequence of neural image processing.

It certainly has to be, but the interesting question is whether it is early or late...

At one "early" extreme you have the fact others have mentioned that we sense light through the combination of the outputs of 3 types of colour receptors, each with its own response/wavelength curve (approximately a normal distribution for each, and they overlap)

Then there is the processing that occurs between retina and higher level cognition, a considerable amount, in fact.

Then, there is the possibility of a relatively high level of processing, in that we often form mental models that somewhat artificially divide aspects of reality into "chunks", because it is a useful simplification.

[subversive science]

From what I understand, it's an issue of perception. As you said, we form mental models of the world, in many cases to simplify what we experience.

[mistermack]

Maybe it's because you're not looking at a rainbow right now, you're going from memory.
And you have more memories of PICTURES of rainbows, than you do of rainbows.

It's one of the first things that little children paint, and you always paint discreet bands, because you have discreet colours in your paint-box.

I don't think that real rainbows look stripey. But they don't look like a blur, either. I think our brains pick out differences, rather than similarities. So we look at and register the contrasts more than the blurred bits. So although you SEE the complete graduation from red to yellow, your mind picks out the contrast between the red and the yellow, and ignores the bit between.
Different people respond to different actual colours, I believe. I personally see the most contrast between red, yellow, green and blue, with all the others less distinct. So even in a perfectly gradual rainbow, I'm seeing SORT OF banding, even if it's not actually there.

From an evolutionary point of view, maybe red, yellow and green sensitivity is to do with picking out food, and blue is to do with recognising which way is up, when moving fast through the trees.

[MiM]

I actually looked at a few photographs of rainbows, before asking the question. Some look more blurred and other more stripy, which confuses things even further. Macdocs theory about tricolour vision could be the answer, but then it might be more of a post processing thing too

[subversive science]

It's not because of tri-color vision, as the chromatic peaks of our eyes do not correspond to the colors of the rainbow.

[Audley Strange]

Actually, I'm looking at a rainbow right now outside my window. Seems like blurry gradations rather than definite stripes with yellow being the most vibrant and obvious. However, I do think we have to take into consideration both the perception and our knowledge.

Newton chose to arbitrarily divide the visible spectrum into seven colours out of a belief, derived from the beliefs of the ancient Greek sophists, who thought there was a connection between the colours, the musical notes, the known objects in the solar system, and the days of the week

From wikiwakiwoo.

[macdoc]

But it may be cause of the interaction of the three colors our rods perceive.
Vision is post processing and even if the chromatic peaks are not "centred" the interaction of colour and complentary colour will still occur.
Chromatic peaks are primarily the brightness or intensity like increasing the saturation...the colour is still there at a lower or higher intensity.

Don't think it matters where the intensity peak is...