alek0

Yes, but that is not the signal, that is the noise. If you have a monochromator with a detector which you use for characterizing light sources and if you heat up your detector you will get the signal even if you block the entrance slit. That is noise - signal which does nto correspond to the light input into the detector.

As for measuring color, again - CIE coordinates and correlated color temperature. These are based on purely physical parameters - electromagnetic spectrum measured, while definitions have been derived again pn physical basis - human eye response curve.

Let me put this as simple as possible:
Colors can be measured. No consciousness is needed to detect color. Color can be quite accurately determined by machines by measuring electromagnetic spectrum and performing some simple calculations. Photometric definitions are based on human eye response - nothing mysterious, purely physical, clearly defined and reproducible.

However, it should be pointed out that photometric quantities and units are not physically different from radiometric quantities. They only exist for our own convenience, because they reflect nonlinear response of a human eye. For example blue, red, and green lightsources with same power in W/sr m^2 will not be perceived as same brightness due to different eye sensitivity for different wavelength.

You can argue that color is not a physical quantity in a same sense as intensity of emitted electromagnetic radiation at certain wavelength. But you cannot argue that it isn't purely physical phenomenon, because it is - defined by response of our detection system for electromagnetic radiation with human eye as a detector and brain as signal processing unit.

Volker.Doormann

It is irrelevant how you call that light impression.

The light impression is.



Yes. But that thermal noise exist only in resistive detectors at temperatures greater than 0 Kelvin.

There is no noise in light. Each human eye can observe 1 photon.

But still there is a perception of color with closed eyes to proof using physical dimension in SI units.



I think it is very simple to understand, that a response from a human, relating his color perception, needs the ability of this human creature to perceive color in his consciousness. I think I have stated this some times.



I think it is very simple to understand, that a response from a human, relating his color perception, needs the ability of this human creature to perceive color in his consciousness. I think I have stated this some times.

I argue that every measuring process of electric detectors is based on that, what humans in middle perceive as colors.

In his book: 'The Measurement of Colour' (1969) W. D. Wright, Professor of Applied Optics am Imperial College of Science and Technology, writes on page 112 in the capital: "The Definition of the 1964 Standard Observer":

"Color matching .. functions .. had already beed prepared in 1959 on the basis of the Stiles and Speranskaya measurements, and they were formaly approved by the C.I.E in 1964 as official C.I.E. 10 deg. functions. They were based on the weighted combination of the observations of 49 subjects (34 men and 15 woman) recorded by Stiles and 18 by Speranskaya, and the subsequent extensions of Speranskaya's results to 27 observers(23 women and 4 men) showed little change in her mean set of curves."

From this i think it should be of no doubt, that that, what is written in conventions about technical color calculations are based on that, what is perceived from human consciousness as colors.

If there is no observer, than there is no color. Color is only a state in the consciuosness (of an observer) and has no relation to physics.

Volker

Nowhere357

Surely there can be no objection to this statement. Color is perceived subjectively. That's the point of this thread, the point is correct, so why all the fussing?

Near the top I read "It is only to perceive by the spiritual consciousness of a creature." Ah-ha! The forbidden "s" word! So the fussing was just pre-emptive dogmatic defense, not a pretty sight coming from skeptics.

"Spiritual" need not mean "supernatural". It's a perfectly good word that has been corrupted by religion. Sheesh.

Mageth

Volker:

If there is no observer, than there is no color. Color is only a state in the consciuosness (of an observer) and has no relation to physics.

Others have joined that know far more about the physics and optics than I, but I might add this.

Sometimes, if there is an observer, there is no color.

How does your "spirit theory" account for color blindness? There are, of course, people who can't distinguish among colors (red/green is the most common). There are also people who are totally colorblind, who see only grayscale. In addition, various species range from totally colorblind to fully "color-sighted", some able to distinguish ranges of color outside our abilities, and some able only to distinguish a subset of the colors we can distinguish.

All of this points to a physical explanation for color perception.

In addition, certain types of brain injury can result in loss of the "concept" of certain colors, e.g. one could lose one's concept of "yellow", or even the ability to associate any wavelength one detects with its corresponding "color". There are well-documented cases of such injuries.

So, tell me, how would physical injury result in damage to our "spiritual" ability to perceive/identify color? Our "subjective" ability to identify colors can be interrupted by damaging a particular region of the brain. Sounds rather physical, rather than spiritual, to me.

Nowhere357:

Color is perceived subjectively.

As far as we know, all of us who can see the full range of colors "see" or perceive the same colors, so it's quite possible that color is objectively perceived; i.e. our brains are "programmed" to perceive colors as we do. Otherwise, we'd have to all see the same colors "subjectively", which doesn't make a lot of sense.

Further, as illustrated several times above, color can also be perceived objectively by various instruments. If we can construct an instrument that can objectively perceive colors, then there's no reason to think that our optical system can't be just such an objective instrument.

Feather

Er, not according to m-w.com:

The "point" of this thread is that because humans allocate a collection of sound units (called "words") to a given phenomenon, that it must be "spiritual." In specific, the point is that since "color" (the word) is a creation of the human mind, then "color" (the physical phenomenon) doesn't exist in the physical realm.

There is nothing "spiritual" about color at all. Previous posters have done quite a good job at explaining the physics behind color. Perhaps they've failed to state the key phrase that destroys the "color is spiritual" argument. So I'll recap their statements and add an extra one:

1) light of a given wavelength strikes the rods and cones in the eye
2) The rods & cones send an electrical signal to the optical centers of the brain
3) Chemistry Happens.

That's it. That's the physics behind what goes on when light strikes the eye. Emboldened words are concept with a corresponding unit in SI.

The key statement is this: 4) The resulting perception is given the label "color" by humans. Nothing spiritual. We merely use "color" as a very terse shorthand. Consider these two statements:

1) "That ball is blue."
2) "The spherical shaped matter over there is composed of molecules that reflect more light of near 460nm in wavelength than any other wavelength, and this light has struck the rods and cones in my eye which causes my brain to register the interaction."

They both say exactly the same thing, except the former is more useful for purposes of everyday communication while the latter is an exercise is pedantics that physics students might amuse each other with.

Mageth

Excellent, Feather. :notworthy

I'll add: neuroscience understands quite a bit, and is learning more all the time, about how (and where) our physical brains associate or map a signal (e.g. the electrical signal coming from the eye) to a perceived "color", and then associate a "label" (e.g. "red") with the perceived color. In other words, we're learning more about how our "sight instrument" works. So far, no one's come across any little, necessary "spirits" in there.

eh

Yeah yeah, the perception of "color" exists only in the mind. Photons of various energy levels do not have colors - as they are what cause the brain to generate them. You might say we live in a colorless universe.

But what is so special about that? The same could be said for all the senses. Pain, sound, smell and taste are all caused by real physics, but the perception of these things is entirely based in the mind. Since we have good reasons for believing all of those are caused due to events in the brain, the notion of a spiritual connection is a little out of place.

Nowhere357

Our instruments cannot perceive color - they detect wavelengths and photon counts, etc. I don't think we are in disagreement here; just semantics. We DETECT "color" objectively, and PERCEIVE color subjectively. Well, IMHO.

Mageth

We DETECT "color" objectively, and PERCEIVE color subjectively.

To my knowledge, the most you might say is that we may perceive color subjectively. As far as we know, we all "perceive" yellow etc. the same (unless there is some physical difference in our brain, e.g. due to injury). If we all perceive color the same, our color perception could harldy be called "subjective".

Volker.Doormann

Agree. Thanx for comment.

Volker