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Author Topic: Does light have harmonies and octaves?  (Read 4572 times)

Offline bizerl

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Does light have harmonies and octaves?
« on: 20/01/2013 22:29:34 »
I recently learned (on this forum) that the primary colours are merely just based on what frequencies our eyes pick up the best, and hold no intrinsic value outside our anatomy.

I always thought that harmonics and octaves etc. are intrinsic properties of waves and are true regardless of what the ear's anatomy can detect.

a) Am I wrong?
b) Are there any equivalent properties of light that would be true regardless of the aparatus used to detect and analyse it?


 

Offline Pmb

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Re: Does light have harmonies and octaves?
« Reply #1 on: 21/01/2013 02:51:03 »
Quote from: bizerl
I recently learned (on this forum) that the primary colours are merely just based on what frequencies our eyes pick up the best, and hold no intrinsic value outside our anatomy.
I wouldn’t put it that way. The light spectrum itself is broken up into primary colors. Pass sunlight through a prism and you’ll see it break up into the different colors. This is more than simply being related only to physiology.

Quote from: bizerl
I always thought that harmonics and octaves etc. are intrinsic properties of waves and are true regardless of what the ear's anatomy can detect.
Harmonics pertain to waves, regardless of what kind of wave it is. Many oscillators, including a Cepheid variable star, are periodic and as such composed of harmonics. However octaves pertain specifically to music.

Quote from: bizerl
a) Am I wrong?
Yes.

Quote from: bizerl
b) Are there any equivalent properties of light that would be true regardless of the aparatus used to detect and analyse it?
I’d answer that by saying that properties do not exist independent of measurement since measurements pertain to what is observable and if something is not observable then I wouldn’t say that it’s a property.
 

Offline bizerl

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Re: Does light have harmonies and octaves?
« Reply #2 on: 21/01/2013 04:35:16 »
Quote from: bizerl
I recently learned (on this forum) that the primary colours are merely just based on what frequencies our eyes pick up the best, and hold no intrinsic value outside our anatomy.
I wouldn’t put it that way. The light spectrum itself is broken up into primary colors. Pass sunlight through a prism and you’ll see it break up into the different colors. This is more than simply being related only to physiology.

But "primary colours" only work because we have three colour receptors. It's only a trick of the measuring. If we had 6 colour receptors, there would be six primary colours. I thought the problem with colour-blindness was that they only had two receptors which means two primary colours for them.

Quote
Quote from: bizerl
I always thought that harmonics and octaves etc. are intrinsic properties of waves and are true regardless of what the ear's anatomy can detect.
Harmonics pertain to waves, regardless of what kind of wave it is. Many oscillators, including a Cepheid variable star, are periodic and as such composed of harmonics. However octaves pertain specifically to music.

So when a guitar string vibrates and gives a note, then you half the length of the string (essentially doubling the frequency of the sound wave), you get the same note, but an octave higher. The note repeats itself each time you double the frequency.

If a light wave has a certain frequency, and you double it, are there any properties that repeat?
Quote

Quote from: bizerl
a) Am I wrong?
Yes.

Quote from: bizerl
b) Are there any equivalent properties of light that would be true regardless of the aparatus used to detect and analyse it?
I’d answer that by saying that properties do not exist independent of measurement since measurements pertain to what is observable and if something is not observable then I wouldn’t say that it’s a property.

I guess what I'm asking is if there is any property of light and colour that would be the same for us as it would be a papilio butterfly which apparently has six colour receptors?
 

Offline RD

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Re: Does light have harmonies and octaves?
« Reply #3 on: 21/01/2013 06:04:28 »
I guess what I'm asking is if there is any property of light and colour that would be the same ...

A particular colour is not perceived by "us" as the same in different contexts ...
http://www.thenakedscientists.com/forum/index.php?topic=44593.msg391299#msg391299

The human eye (or rather brain) is fooled by the above optical illusion, but a scientific instrument to measure colour wouldn't be.
« Last Edit: 21/01/2013 06:11:34 by RD »
 

Offline evan_au

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Re: Does light have harmonies and octaves?
« Reply #4 on: 21/01/2013 11:55:59 »
An "octave" represents a doubling of frequency.

Doubling the frequency of a tone (or 4x & 8x the frequency) produces "harmonics", and happens naturally when you pluck a guitar string, blow a saxophone, turn up the volume too high on your sound system, or in general do almost anything to distort a pure sine wave (other things that you can do by distorting a sine wave will produce odd harmonics, like 3x & 5x the frequency).

As long as you don't distort a sine wave too much, these harmonics sound harmonious to the human ear. (Heavy Rock enthusiasts might contend that you can't distort a sine wave too much!) Two tones an octave apart are very harmonious to the human ear, triggering hairs of related resonant frequency in the cochlea (the full reasons are not obvious, and may involve physiology of the human ear, formants in human speech, human brain structures and early exposure to music styles).

The octave is a very useful concept in music. A typical piano keyboard spans a bit over 7 octaves, while human hearing spans even more octaves, both higher and lower in frequency.

An octave is not a useful concept in human vision, because human vision has a very limited range - equivalent to a keyboard containing just 3 notes, spanning less than 1 octave (reduced sensitivity extends somewhat outside the peaks, allowing about 1 octave).
  • There are few optical materials which have sufficient non-linearity to produce visible amounts of red photons from violet photons at twice the frequency
  • Producing 1 violet photon from 2 red photons is possible, but is not energetically favourable
  • The nearest we experience is phosphorescence (eg in fluorescent lamps), where an ultraviolet photon strikes a phosphor compound, exciting other lower frequencies which are not harmonically related.
  • Any frequency relationship would not be visible to us, because we can't see the incoming ultraviolet photon.

Non-linear effects do occur with light, and are sometimes used to produce laser light of a different frequency. They also cause problems in optical communication systems, so steps are taken to use linear optical materials, and to keep the power levels low enough so these materials do not become non-linear.

The reason humans see about 7 colours in the spectrum is because we have 3 colour receptors in our eyes, which are stimulated to different amounts by the continuous spectrum produced by a rainbow.

Even with this very limited range of human vision, there are certain colours which are considered harmonious, and others which are considered clashing, see http://en.wikipedia.org/wiki/Color_scheme (the full reasons are not obvious, and may involve physiology of the human eye, human brain structures, early exposure to art styles, and this year's fashions). As far as I can see, the reasons do not include numerical ratios of the photon frequencies. 

Creatures which have more colour sensors than humans (like the 12 found in this mantis shrimp: http://www.sciencedaily.com/releases/2008/05/080513210456.htm ) will see far more than 7 colours in a rainbow, including some which are more than an octave apart - not that we have much hope of getting a mantis shrimp to describe these hundreds of colours for us!
« Last Edit: 21/01/2013 12:02:05 by evan_au »
 

Offline evan_au

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Re: Does light have harmonies and octaves?
« Reply #5 on: 21/01/2013 12:18:18 »
Humans are considered "Trichromats", with 3 light sensors.

Some people called "Tetrachromats" are born with 4 colour sensors (and it should be somewhat common amongst women, because one of these sensors is coded on the X chromosome, and women have two X chromosomes, sometimes bearing different gene variants).

These extra sensors are not always functional in revealing different colours, perhaps for physiological reasons, and perhaps for psychological reasons (they are always told that all these colours are red, even though they look different).

For an account of this and other visual effects, listen to:
http://www.radiolab.org/2012/may/21/perfect-yellow/ especially starting around minute 4:00
also http://www.radiolab.org/2012/may/21/
« Last Edit: 22/01/2013 09:31:39 by evan_au »
 

Offline Pmb

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Re: Does light have harmonies and octaves?
« Reply #6 on: 21/01/2013 15:05:12 »
Quote from: bizer
But "primary colours" only work because we have three colour receptors. It's only a trick of the measuring. If we had 6 colour receptors, there would be six primary colours. I thought the problem with colour-blindness was that they only had two receptors which means two primary colours for them.
Good point. Thanks for correcting me.
 

Offline syhprum

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Re: Does light have harmonies and octaves?
« Reply #7 on: 21/01/2013 15:12:38 »
Newton was an enthusiast for the occult which lead to him naming a seventh colour for the rainbow i.e indigo
 

Offline AndroidNeox

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Re: Does light have harmonies and octaves?
« Reply #8 on: 21/01/2013 17:48:59 »
Insightful question...

Yes, light, like all wave forms, has harmonics. When you look at an oil slick on water, you'll see the same colors in successive rings even when the oil is getting steadily thicker or thinner. At each location that the optical path length through the oil is a harmonic of a specific color, that color will appear.

In fact, lasers operate like resonance chambers... think organ pipes. You stimulate them and they resonate in whatever frequency they are tuned for.
 

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Re: Does light have harmonies and octaves?
« Reply #8 on: 21/01/2013 17:48:59 »

 

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