Exploring the Nature of Light and Color

In summary: I think rbelli1 is making the case that because visible light is the range of frequencies that our eyes can detect, it is the range that is most important for organisms to detect.In summary, Dave thinks that there are particular qualities of EMR that differ one from the other depending upon essential properties such as frequency or amplitude. He also thinks that there is something special about the frequency range of "visible light" that makes it more likely organisms would evolve the capacity to detect it.
  • #36
David Lewis said:
Until recently, it was both. Scholars analyzed ancient texts that listed the colors of everyday objects. The color of the sky was usually recorded as bronze or gray, so it was hypothesized that blue and violet are recent colors. Now it appears there may have been cultural and linguistic distortions regarding the concept of colors. To the Greeks, for example, "color" encompassed physical qualities (textures, smells) and emotions -- not just a certain frequency of light.
Colours and how they are described and appreciated are very much a part of culture. Notwithstanding that, I would strongly suggest that an ancient Greek would make the same sense of a good colour TV picture as would a modern TV owner. The Engineers have managed to separate culture from perception in quite an impressive way.
 
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  • #37
sophiecentaur said:
Colours and how they are described and appreciated are very much a part of culture.
Good point. What we mean by "color" may not fit the same definition as that of pre-scientific people.
 
  • #38
Human vision is evolved to take advantage of a particular window in the atmospheric absorption spectrum. Take a look here
https://earthobservatory.nasa.gov/Features/RemoteSensing/remote_04.php
We can see in the spectral region where the sky is mostly clear. It's because we are daytime animals (for the most part) and live above ground. Also, note that the solar spectrum is also peaked in intensity around green, so the visible region is optimal in terms of brightness.
 
  • #39
Graeme M said:
Sorry, I meant the photoelectric effect. What I'm getting at is that when I think of eyes evolving, I note that generally they seem to work only for a limited range of frequencies - visible light, some IR etc. But what is it about those frequencies that led to eyes evolving. Reading about the photoelectric effect tells me that there are behaviours that are tightly related to frequency, so is there something special about the frequency range of "visible light" that makes it more likely organisms would evolve the capacity to detect it? Why not some other frequency? Why not gamma rays?

Graeme M said:
Ah, excellent, that all explains it very well. Thanks to all who offered comments, very much appreciated.
One further comment. Light itself is not actually visible. I'm specifically referring to visible light. Although light is detected by the eye, we only detect light that actually strikes the retina. Not light that passes by us. Detection through physical contact, even if it's by the eyes, falls in the category of touch, not sight. We detect (feel) light with the eye but we see through the eye. Visual perception actually occurs in the brains visual cortex. Here's where the brain creates images of the objects (from which the light originated).

http://www.cycleback.com/eyephysiology.html

Check out page 112 of The book of general ignorance.
 
  • #40
Technically all our senses are "touch" then, aren't they? Receptors respond to physical contact in some way and generate electrochemical signals to the brain where specific regions decode these. This results in what we describe as perceptions, or awareness of the world. It couldn't be any other way, could it?
 
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  • #41
That's an excellent point. I never thought of it that way. All our senses are based on touch. But we don't perceive the thing that touches us. We perceive what our brain creates in response.
 
  • #42
Graeme M said:
Technically all our senses are "touch" then, aren't they? Receptors respond to physical contact in some way and generate electrochemical signals to the brain where specific regions decode these. This results in what we describe as perceptions, or awareness of the world. It couldn't be any other way, could it?
That is not a very good way to look at things. Light sensors do not depend on any physical displacement and surely that is what is means by "touch". Sound sensing depends on physical displacement (vibrations) but thermal sensors, like light sensors, do not respond to movement and nor do chemical (smell / taste) sensors.
 
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  • #43
Well, no, I mean "touch" in the sense that Furyan5 seems to be using it. We call the act of making a physical contact between an object and our fingers (for example) "touch" but at some level it is a physical interaction between the receptors in our body and the physical environment. Whether we are reacting to photons, or vibrations, or pressure, or molecules locking into receptors, at the most basic level all senses are our receptors reacting to a physical interaction with our environment. So all sensing, in that sense, is "touching" our environment, and causing some internal model or representation of the thing we touched. No representation is the thing itself, it is only an inner response to the exact same set of signals from our receptors which depend upon the touch of the external environment to enable this.
 
  • #44
Graeme M said:
Well, no, I mean "touch" in the sense that Furyan5 seems to be using it. We call the act of making a physical contact between an object and our fingers (for example) "touch" but at some level it is a physical interaction between the receptors in our body and the physical environment. Whether we are reacting to photons, or vibrations, or pressure, or molecules locking into receptors, at the most basic level all senses are our receptors reacting to a physical interaction with our environment. So all sensing, in that sense, is "touching" our environment, and causing some internal model or representation of the thing we touched. No representation is the thing itself, it is only an inner response to the exact same set of signals from our receptors which depend upon the touch of the external environment to enable this.

Thank you, you're the first person I come across that actually understands the point I'm trying to make. We don't actually see light, we see because of light. Our brain doesn't create a visual representation of light itself, for us to perceive. The brain interprets light into sensations such as colors and brightness. It's this we perceive. It's through colors and brightness that we perceive objects. The contrast from its surrounding colors and brightness.
Once again, thanks.
 
  • #45
Graeme M said:
Well, no, I mean "touch" in the sense that Furyan5 seems to be using it
If you go back a few hundred years, they had the 'Tactile' Theory of Light, in which it was thought that a sort of tentacle came out of our eyes and touched any object that we 'saw'. Whilst that could well be the way that people feel they are seeing things (the mind is weird and wonderful) it really is a poor model and falls down as soon as you consider large distances and the propagation speed (if not long before).
However, it is true that looking at a cuddly puppy will stimulate tactile memories about puppies in general and seeing a rough stretch of icy water will make us feel chilly. I would say that relates to the way our individual minds work and it is difficult to lay down any law about how the 'next person' is perceiving things.
 
  • #46
sophiecentaur said:
If you go back a few hundred years, they had the 'Tactile' Theory of Light, in which it was thought that a sort of tentacle came out of our eyes and touched any object that we 'saw'. Whilst that could well be the way that people feel they are seeing things (the mind is weird and wonderful) it really is a poor model and falls down as soon as you consider large distances and the propagation speed (if not long before).
However, it is true that looking at a cuddly puppy will stimulate tactile memories about puppies in general and seeing a rough stretch of icy water will make us feel chilly. I would say that relates to the way our individual minds work and it is difficult to lay down any law about how the 'next person' is perceiving things.

We agree that an object is red. It's irrelevant whether we perceive the same thing. Understanding that we may not, is the issue. Light is merely an information carrier. Our brain interprets the information, forming visual perceptions which we perceive internally. The reality you see is not "out there". It's a simulation which exists in your head and your brain is the simulator.

 
  • #47
Furyan5 said:
We agree that an object is red.
I don't think that is, in general, true. Cultures differ in how areas of the CIE chromaticity chart are grouped and perceived. It is probably true to say that different people will agree (broadly) that a particular colour on a TV screen matches a given object. In fact Colour TV is pretty successful around the World, despite the fact that people have different 'names' for their colours. I am not talking here about Language, as such, but about the context and importance that different people assign to a particular 'colour' (as defined by RGBY values).
 
  • #48
Are you talking about emotional responses to colors? Or understanding what colors are and how we see them?
 
  • #49
Furyan5 said:
Although light is detected by the eye, we only detect light that actually strikes the retina. Not light that passes by us.
Very true, but if a searchlight beam travels through dust, the beam will stand out. A small fraction of the beam is scattered, so indirectly, you know that light is passing you by.
 
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  • #50
Furyan5 said:
Are you talking about emotional responses to colors? Or understanding what colors are and how we see them?

It is the definition of "red". Go to a home-improvement store, look at the paint department, and see how many different "reds" there are.

I am a bit surprised that there aren't more quantitative aspect of this discussion. I know that the topic is centered on "seeing" light, as in visible light, using our human eyes. But why hasn't there been any attempted to actually define this through specific wavelength or frequency of that light? After all, this is one surest way of distinguishing EM radiation. You may call one color red, while another person may call it "pinkish red" or "wine red", but no one will argue if we categorize them instead by their wavelengths. It is the least ambiguous way to define any EM radiation.

Or is it because our eyes can't actually spit out these values that we are not going to consider such quantitative description? But what's wrong with using an instrument to detect such values?

Zz.
 
  • #51
David Lewis said:
Very true, but if a searchlight beam travels through dust, the beam will stand out. A small fraction of the beam is scattered, so indirectly, you know that light is passing you by.
It's not the beam of light you see, it's the dust in the path of the beam that becomes brighter. The beam itself is undetectable unless it strikes your retina. Then it becomes detectable, not visible.
 
  • #52
ZapperZ said:
It is the definition of "red". Go to a home-improvement store, look at the paint department, and see how many different "reds" there are.

I am a bit surprised that there aren't more quantitative aspect of this discussion. I know that the topic is centered on "seeing" light, as in visible light, using our human eyes. But why hasn't there been any attempted to actually define this through specific wavelength or frequency of that light? After all, this is one surest way of distinguishing EM radiation. You may call one color red, while another person may call it "pinkish red" or "wine red", but no one will argue if we categorize them instead by their wavelengths. It is the least ambiguous way to define any EM radiation.

Or is it because our eyes can't actually spit out these values that we are not going to consider such quantitative description? But what's wrong with using an instrument to detect such values?

Zz.

That's because color is not a direct interpretation of wavelength/frequency and amplitude. There are other physiological factors involved as well. Google the strawberry illusion. The strawberries look red but there is no "red" light. A "red" balloon looks "black" under "blue" light. There are many such examples. Colour isn't fixed by a lights particular wavelength/frequency or amplitude.
 
  • #53
Furyan5 said:
The beam itself is undetectable unless it strikes your retina. Then it becomes detectable, not visible.
Good point. Visibility refers to raw sensory input. Detection involves reasoning.
 
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  • #54
David Lewis said:
Good point. Visibility refers to raw sensory input. Detection involves reasoning.
Correct. Without the brain to interpret the data from the eyes, nothing is perceived.
 
  • #55
Furyan5 said:
That's because color is not a direct interpretation of wavelength/frequency and amplitude. There are other physiological factors involved as well. Google the strawberry illusion. The strawberries look red but there is no "red" light. A "red" balloon looks "black" under "blue" light. There are many such examples. Colour isn't fixed by a lights particular wavelength/frequency or amplitude.

"Color" is a handwaving human characterization of EM radiation that human can see. "Wavelength" is a more definitive characterization of EM radiation that isn't affected by "physiological", social, cultural etc. factors. So why not deal with that?

Zz.
 
  • #56
ZapperZ said:
"Color" is a handwaving human characterization of EM radiation that human can see. "Wavelength" is a more definitive characterization of EM radiation that isn't affected by "physiological", social, cultural etc. factors. So why not deal with that?

Zz.
What exactly do you mean by "deal with that"? You're welcome to start a thread concerning wavelengths and what concerns you about them. In regards to this thread, they play no relevance.
 
  • #57
Furyan5 said:
What exactly do you mean by "deal with that"? You're welcome to start a thread concerning wavelengths and what concerns you about them. In regards to this thread, they play no relevance.

Read the rest of Post #50 on why I find this thread puzzling and why the quantitative aspect of it has been ignored.

Zz.
 
  • #58
To be honest, I don't understand that post. Unless you believe light itself has color.
 
  • #59
Furyan5 said:
To be honest, I don't understand that post. Unless you believe light itself has color.

OK, one more time:

1. "Color" is a human invention. It is a sloppy and ambiguous way of characterizing EM radiation.

2. "Wavelength" and "frequency" of EM radiation are more direct, clear, and definitely less ambiguous. So why aren't you including the discussion of different types of EM radiation using such characterizations rather than just using "colors"? It is why I asked if you are only restricting yourself to using the human eye as the sole light detector.

Is this clearer now?

Zz.
 
  • #60
Graeme M said:
Well, no, I mean "touch" in the sense that Furyan5 seems to be using it. We call the act of making a physical contact between an object and our fingers (for example) "touch" but at some level it is a physical interaction between the receptors in our body and the physical environment. Whether we are reacting to photons, or vibrations, or pressure, or molecules locking into receptors, at the most basic level all senses are our receptors reacting to a physical interaction with our environment. So all sensing, in that sense, is "touching" our environment, and causing some internal model or representation of the thing we touched. No representation is the thing itself, it is only an inner response to the exact same set of signals from our receptors which depend upon the touch of the external environment to enable this.
I'm sorry, but this just doesn't seem very meaningful to me. In order for things to interact (except perhaps in QM), they have to be co-located. So what? Or is that the whole point?
 
  • #61
Furyan5 said:
We don't actually see light, we see because of light. Our brain doesn't create a visual representation of light itself, for us to perceive. The brain interprets light into sensations such as colors and brightness. It's this we perceive. It's through colors and brightness that we perceive objects. The contrast from its surrounding colors and brightness.
Well, we "see light" in the sense that photons themselves hit photosensors and trigger a response.
 
  • #62
Furyan5 said:
Are you talking about emotional responses to colors? Or understanding what colors are and how we see them?
Everything in our minds is 'emotional' to some extent. Everything we experience is subjective. We invented Mathematics as a way of communicating in a very formal way and we have agreed on the syntax and 'meanings' it carries. But when we try to communicate any of our sensations to another individual, we are limited to our language or to real life examples (eg red is like strawberries and coke bottles - no use for someone who has seen neither).
We 'understand' (a dodgy word in most contexts and even more so in psychology) that colours can be mimicked and measured up to a point so we can sort of reverse engineer human colour vision. whether or not that involves understanding of the process is questionable. Colour is only really in our heads. Outside of our heads, we can only use a model that can predict reasonably well what colour a human will assign to a given spectral mix on a screen.
 
  • #63
ZapperZ said:
OK, one more time:

1. "Color" is a human invention. It is a sloppy and ambiguous way of characterizing EM radiation.

2. "Wavelength" and "frequency" of EM radiation are more direct, clear, and definitely less ambiguous. So why aren't you including the discussion of different types of EM radiation using such characterizations rather than just using "colors"? It is why I asked if you are only restricting yourself to using the human eye as the sole light detector.

Is this clearer now?

Zz.

The thread is not about whether we detect light or not. Everyone agrees that we detect certain wavelengths. The thread is about whether we perceive light or not. Is the detection of light by the eye called seeing when all other visual perception occurs in the visual cortex. Is detecting light, seeing or only a part of the process which results in seeing. Opinions seem to differ, so I'm seeking clarity, with an explanation, why people believe one or the other.
 
  • #64
The human eye is not a spectrometer and our appreciation of the spectrum of the light we see is only based on a very crude analysis. Only three basic broadband analysis filters have been identified but our vision system makes good use of that data and context to come up with a highly data reduced measure. It's good enough for us to have survived ok and that's all that evolution needs to provide us with.
There is a lot of very sloppy terminology around - even on PF - which refers to the 'wavelength of colours'. I am always surprised that the basics of tristimulus colour vision seem to be too much for many otherwise bright people to take on board.
 
  • #65
russ_watters said:
I'm sorry, but this just doesn't seem very meaningful to me. In order for things to interact (except perhaps in QM), they have to be co-located. So what? Or is that the whole point?
Answered in #64
 
  • #66
Furyan5 said:
The thread is not about whether we detect light or not. Everyone agrees that we detect certain wavelengths. The thread is about whether we perceive light or not. Is the detection of light by the eye called seeing when all other visual perception occurs in the visual cortex. Is detecting light, seeing or only a part of the process which results in seeing. Opinions seem to differ, so I'm seeking clarity, with an explanation, why people believe one or the other.

This does not sound like a physics question. It is more physiological, biological.

Zz.
 
  • #67
Thanks to everyone for participating. This thread is slowly going off-topic, so it is closed.
 

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