About science; About color vision

This is about science produced by the California Institute of Technology and originally broadcast by station KPCC Pasadena California. The programs are made available to this station by national educational radio. This program is about color vision with host Dr. Albert Hibbs and his guest Dr Richard Feinman Nobel laureate and professor of physics at Cal Tech. Here now is Dr. here. Ever since Isaac Newton used a toy prism to turn sunlight into a rainbow of colors. Scientists have known that white light is really composed of a complete spectrum running from dark red to deep violet. We know that each color in the spectrum can be identified by a particular number which gives the frequency a little light that makes the color. But with all this knowledge about the physical basis of color it's still not possible to predict some of the interesting ways in which the human eye and the human mind respond to color. And this difference the difference between a physical description of light in terms of frequencies and the human perception of color

is our subject tonight our guest is Richard Feinman of Caltech. Dick let me start out by asking you this different colors correspond to different frequencies of light different musical notes correspond to different frequencies of sound waves so wouldn't it be possible to get some understanding of color in terms of an analogy between sound and color between musical notes in different colors. I've got to back you up a bit. All right. Back up. That's what usually people think in say different colors cars by the different frequencies of light. But this is a much more complicated situation. When you look at something to decide what the color of the thing is it doesn't depend so directly on the light that caused that particular spot as you might think. So you mean if I see light of a particular frequency that I mused to saying is that in the red end of the spectrum I would always call it red the red is nearly always red if it's pure but it's a an agreement might look like white it

might look like blue. It could look like brown. That much difference than yes for it's a red speck of could look like chocolate color. OK how much of it are not complicated I don't want to say that the spectrum has these colors that I would go back a little bit and say for the fifth right point of view. When you spread the light out there's different kinds of light physically different kinds of light and your analogy is a good one will correspond to like high notes at the blue end of the spectrum and the other corresponding low notes like the red end of the spectrum what we call the right and right but in the is a very interesting other difference and that has to do with mixing. Suppose that I shine in the same place two bits of spectrum light. OK I was going to two different wavelengths that would correspond to heavy in the ear at the same time. Two notes being played in the piano simultaneously. But in the year you hear these two distinct as two not as two notes and in the eye if you looked at say a mixture of two different kinds of light you'll see a different color but you won't see those two

distinct forms when we just know you don't well you can't tell us what the two were that went together to make that call. Like in the year you can still hear if you're clever or they tell me my year isn't so good. They tell me that you can still make out the two individual notes. But even worse let me go in for OK. It turns out that there is a ways of fooling the eye and it can't have it so I was going to explain it in this way I can take different distributions of life like I take some from one part of the spectrum and some from another and some from another mix them together like a painter mixing thanks to sis. Well let me just mix the lights will come to what a painter but very much like a painter mixes paints but you're not mixing paint my mixing light I'm shining. Yes right. Different kinds of lights together. Then I get some kind of an effect on the eye. Now it turns out there may be another mixture. Completely different bits of the spectrum might be used mixed together in certain proportions. That is absolutely indistinguishable by the I the thing that would happen

in a year would be if someone would play three notes on a piano. And then by fishing around on the scale you. Find three other notes say for instance that he could play that you couldn't tell it was different in the first reply and that doesn't happen now than happened with sorrow but it does we can analyze a sound with far more detail and much closer to the detailed physical property than the eye can tell the ick and seem like it is. You cannot distinguish all of the details of the way that light is physically form. There are many different. Different ways of physically forming a light that look exactly the same to the eye so you can use different sets of Primary Colors and I stand by again is that what you're talking about. Now the mixing of Primary Colors to produce a a color. Yes as a while if you take any three parts of the spectrum say red green blue dots then put some kind of way of shining just a bit of this red bodies we should say more exactly one wavelength of the spectrum with another wavelength than another wavelength and I adjust the

amount of each is free and I can image that any sensation any light of any kind it's made by mixing any other spectra of light or any other light whatsoever. In other words and if I start out with a different set of three I can do the same thing. Yes any SAT or other some rules about what particular kind you can find out Of course if you have one of the inspector many set there's some complications we always complicate I'm going to make it out what the proposition is so first and again we get to the complicated. Let's take a definite set of 3 8 doesn't make games what you choose but choose three parts of the spectrum so you need to read and get a green book somewhere right. And you'd like the light from the each of these sections through but police are going to screen all the rest of the light is taken out in just these three and you have adjustment that you can put different reports like a colored glass in front of a light or something like that yes you could also do it just as well. What I'm talking about by taking three lamps and putting a piece of glass that's red in

front of one of the sequester screen on another piece of glass it's blue in front of another and have some way to adjust the brightness of the lamps and shine all these three lights on the same. Place. Now if you take any of them might like to take a railroad man signal lamp or something and shine it. I can imitate the light of the railroad men single I have. Exactly so that the eye can't see your eye can't see the difference in that light by adjusting the amounts of the three the red green in the blue. But sometimes I might need a negative amount of one of the lights in order that it may not my going backwards so it sucks light up. It might be a little hard to accomplish. Can you explain what you mean by a Yankee dollars amount. If you took I suppose that when I want to imitate is a very bluish light you say for example ok and the blue and I happen to be using is more close to green. So my blue in my green can make us only in the greenish blue region and adding red isn't going to make it blue.

It makes the yellows orange and makes it work. I'm trying to imitate blue then I can get there with these grooves in Queens for instance. But if I would like to suck some red out offerings I might take some blue and suck some green out the best way to do it way I might be able to do is to take the green away amp that I'm using and shine it on the other side. Mix the green light with the X that you're trying to match. Then the rematch result I can mix with blue and red. It's like putting it on the other side of the equation instead of saying x is equal a certain amount of red plus a certain amount of green processing amount of blue in this case it would be x plus some green can be imitated by blue and red. And that's what we mean by we say. That we can do it with three colors but some times the amount of one of the must be negative. But still you could take. You could have started with an arbitrary three colors and solve that equation. That's right and then it can be done with any three colors and the three lights with one minor exception. If one of the lights could be imitated by mixing the other two

then the you know anatomy thing doesn't it. So you have three lights which is subtly this think that when you go back a minute to something I mentioned just a little earlier about the mixing of paint. You said that isn't what you're talking about what's the difference between mixing from the primary colors to paint mixing the light you're talking about now with it analyzing the light that we're talking about a light that we see see what we see is the stuff that comes into the yard. I Know How It Got That Way. Depends upon what happened to it on the way. For example the light that comes into the eye say that from a leaf. Is not the light of the sun on modified with the light of the sun modified by the colored pigments in the leaf in particularly if we flex very little red out of the short wavelength and the long wavelength and the spectrum a lot of the other and and so it appears a different color a light reaching the eye is different than the light of the sun.

Now pigments paints and dies and so on are simply ways of arranging to modify the light of the sun or whatever on a light or using like the light of the illumination of the room so that the light that reaches the eye is something all right. So when you mix paints is quite a different thing and mixing lights because when for example suppose you take a blue and yellow pigment as every child knows you get green right mixture right. But if you take blue and yellow light and shine it together on a place it looks like white but green has no green look at all I see. Really something quite different quite frankly lights out of colored light bulbs in the result of mixing. Yes the reason is that yellow paint is a paint which takes out the red end of the spectrum and leaves the Greens and the blues and everything together and it looks yellow to us. These yellows and greens and blues. Now blue paint is something that takes out the yellow and the

red of the spectrum and just leaves the bluish and greenish part of the spectrum come to your eye. If you mix the both paints or let's say easier than mixing both things imagine two pieces of cellophane one in front of the other one which is green and one which is one which is blue and one which is yellow the yellow one lets throw everything but red. The blue one on top of it will let through would take away the yellow part of the spectrum and leave just the green the green in the blue and it has an excess of green. So it's a different kind of proportion it's not like adding it's taking away. I see one of the techniques Oh yeah you must take out take pieces of the spectrum because they don't reflect it I don't let it through. Whereas when I put in the lights to get I'm adding it to like I'm letting both come whereas the other way I see a double subtraction sort of like take both I take away is very very different so even though you could match a pigment with it with shining lights when you go into the addition business doesn't work out anymore because you know it is that's rationing when you do with pigments.

That's right and that is what we're going to see another interesting effect which I should mention because otherwise you get confused a bit. If you're not already a lot of use and there's a following. I said that we could imitate two lights exactly by mixing by say at one. Any all light like a radio signal lamp and the other one is a mixture of this red green and blue for instance from the spectrum. OK. And those two lights if they enter the eye would be identical but they shine on a piece of something like a green leaf. You could tell the difference. How so. Because the leaf takes out different amounts of different parts of spectrum for example it takes out some of the red say. So since my distributions although they appear to the eye the same after I take out the red They don't appear to the eye the same. I see so when they started with red only you'd get a different thing when you just cut down the red by reflecting off agree of a green leaf. When you start with all three you cut down the red to leave the others almost full strength but the point is that two things which

look the same to be are I because they have a certain distribution of the different colored lights. Will their distributions will be changed in a different way by then absorbed by the green. So that to cut two things light would look equivalent on white paper will not produce equivalent will not necessary look at equivalent when reflected from a colored piece of paper. Are there different this always has to do nothing with the eye. Well what about the you know it has to do with you see thing we can figure out. It has to do with how the light bounces from all the objects and all physics is easy to figure out is completely definite to figure out in any circumstance exactly what this depiction of all the parts of the spectrum is coming into the on. The interesting question then is. Forget the physical how it got into the eye when it's cut into the eye and you know what's coming into the eye what the time and write happens much wider never just going to different cells respond to each different color how it was not exactly known. The simplest theory which explains these businesses about mixing colors is that there are three different kinds of cells that have three different kind of pigments in

them. Let me explain how it might work. First it was color blind. OK so then we see that they will figure out how to color works all right. All right. Suppose that you had a thing in the eye as a cell. You know some chemical in the cell and when light shines on it chemical changes the chemical. When a chemical is changed. Nerve impulses go off. OK that's not necessarily exactly the way it goes but it's a view from which you can understand everything so quiet now. So the nerve only can know how much chemical has been converted it doesn't know anything else about the light except what the light did namely chew up this chemical and make a new car in which the noise feels right. OK. But different colored different parts of the spectrum may be an equally effective like for instance let's suppose that red light doesn't affect the chemical at all. Right end of the spectrum in the yellow and in the blue and affected pretty yellow and green and spiders

being affected pretty well but the blue doesn't affect it very well. For instance then if we look at something which had a lot of energy in the long end of the spectrum it wouldn't look very bright because not much chemical is being transformed if we used then a little green light we can transform the same amount of chemical. So a little bit of green would look exactly the same as over as a lot of rain to that particular cell to that particular cell because all that thing sees. So to speak is how much of this chemical is transformed. And it has no way to know that it was transformed by red light or by green light. So here we have a theme very crude in the sense that this music with no noise it would know the pitch the same way with no light. But it doesn't know the colors. It's more sensitive to one kind of light than to another but it now is only light. OK now I want you to imagine another sound almost approach that's a color blind eye it has only one kind of pigment which we may say green sensitive.

Not as of right now I suppose that this guy also has other cells with a different pigment and I suppose for definite is to make it easier understand it this pigment is sensitive in the red for red light and not very sensitive which partly says that even the green is not sensitive to the blue say OK so now you know once I once asked me to Greener you brought in one of the sensory direct That's right right. They both work pretty much with the same mechanism but once you do it for the red light and the other for the grass right now we want to know can the brain get any clues to the character of the color of the life. I should think so by comparing these the output of these two nurse cells in your mouth right. Because a green light will affect one cell but not the other will affect say the first one I mean you will call a unicycle on b a green light makes a lot of signal on Iain or even less very much less signal in the Beano. Whereas a red light which doesn't affect the a nerve much affects the beam there even more so the brain so to speak has the information available to I mean it's possible for it to figure out that

there's a different character in the light when you shine a red and when you shine a green physical light. If you shine. But now I want to go in between which might affect both of the two pigments equally for example. Then the thing will go off equally. Right now you notice that that can't be distinguished from a combination of red and green from a combination of two lights red physical and green physical like because it affects both pigments equally and both light shining on the pigments would do the same thing. And therefore a light which is in the middle of the spectrum yellow would be physically I mean optically physiologically to the eye exactly the same as a mixture of red and green. And that's what we find we find that we can imitate light with just three and so the guess is what we have in our life three different pigment rather than two lenses as an extra. The idea is the same as just one more. Why don't you three How about taking the opposite ends of the spectrum Violet in a red

couldn't different proportions of those two make everything else in between which you couldn't distinguish you see. But yes you can make everything in between but it would be two dimensions of color. That is to say you could not distinguish between a blue light and a red light in equal strength. And the light that's green in the middle of the spectrum. So you would look green but you would have some I don't know what color it would look like. But the point is that there would be two different physical world cities to two Asians in the world which the eye can't distinguish namely that from this flower is being reflected in an equal amount of red light and blue light war from this flower is only coming out green light. And it would be the more we know about the world the better it is. So one more piece of information sensitivity in the middle third pigment can distinguish a little more for pain as we would have a greater range of color understanding in the sense that things that were physically not the same would be just the

people I see if we had a million of them and we would have a much like the would be like ear again you be seeing all along here and you see a lot of wonderful detail in the world that we may encounter. Yes. Well if a color photograph is made then it is not necessary to use in a color photograph or any particular set of pigments you could use another sentence to reproduce the scene. Rough or not it's roughly speaking because you can get every proportion of the different colored lights human by having different color pigments mixed up in the photographic plate. The trouble is that the minus numbers as I told you the USA can get every color but sometimes you have to use a negative amount of something. And that's not possible and that's not possible with the film. There's no easy way to do that. And therefore if you use certain particular dies you get a greater range of possible colors without using any negative sign. Then if you have another grain or some special combination that works the best time. Yes but none that were in the wider range of what's the best would depend on which colors are the most interesting or important you got to lose

some. And you lose in some sense at least only it's hard to count how many is least. And if there's no one to say I don't want what you want anyway. And then you know actual kind of business there's a technical problems of which dyes are easy to work photographically and so on and so on. So there are various compromises made so you don't get even the best ideal died or why is it whenever you're in a room that has just. Slightly orange light already is light like an incandescent light bulb it certainly is yellow or red in sunlight. Things too look the same car very nearly so that's a very remarkable thing that's important. I mean that's a backless true it's very true it is very important to the distinction to understand distinction between a light which reaches the eye and the color sensation that we see. Remember I said that with a reddish light you might see Brown. Let me give an example how a reddish light you would see brown ok if you have a circle a dark room an absolutely dark room and the only thing a light is coming from is some circle

and its a red light that looks nice and red in the dark. OK but if you will now have another ring outside of the red circle like a target you see the center is exactly the same as it was before with the same light coming from the Red Bull's eye. Red Bull's Eye no red light coming from the bull's eye. All right I'm of this stock but I'm not out of painted walls I know it's a spot that light is coming. Well I don't know how it came but it's coming from the bull's eye. Sent a red light. All right that Iran that we have a regime say why dream in which a white light say there are many combinations of this phenomena but will take white light is coming. Then if the white light is much stronger than the red light it looked like a chocolate brown. The central spot. You see what Brown it is is a place that isn't as bright as this neighborhood around it. Bandit and the colors the different kinds of crowd have to do with the character like it's coming in are a Jewish thing is a different type of brown we have is riber idea of

different beautiful bronze that comes from having different colored lights but the character that makes it Brown is the has to do with the general illumination and background and so on you know that that's a relatively dark area but some colors some light is coming from compared to the surroundings so there's not not an absolute then I don't imagine brightness is always compared to what's going on what's next there are going. Exactly and it's in this sensation that we get from lights come from looking is not just dependent on the light but how that light appears relative to its neighborhood. So if I just turned on the lights in a room that has that has a something red on the wall it won't turn brown because everything else is down to as a good example. That's right exactly I mean in the light princes from a from a bright orange wall in the ordinary lit room if you could just keep that isolated taken away that light and surround it by a much brighter white light it would look dark.

One of our state of ours to get take greenish yellow for instance ice greenish yellow light and then put a white background a stronger that it right and you get this sort of a dirty greenish color like the army uniforms. Carrying. Well ma'am how uncertain is it not possible however to pick some sort of illumination in a room that will make all the colors change somehow. Not unless you make a very very severe aluminum is like completely red or some such thing it has not got a wide distribution of colors in it. If I just change from one color like to another home within a room I want it but you'll know that I'm for the moment when you change it. But if the light is not very severely colored than extreme that it will be lost I'll see the full range of colors even though I've changed like that shining on it. I visited a land just landed at the power company. He's the one who wrote an article about this and scientific Americans on a lot of experiments with the

feature of what is the sensation that you see in given circumstances of illumination and light coming to the eye. Usually people who do experiments and psychology of this theory they add artificial situations a very simple like a circle of circles. Yeah yeah. And they have noticed a number of the effects that I just talked about that the light the colors look depend upon the illumination. But it turned out in a real situation or a complicated situation the facts are enormously most powerful than had been realized before actually and he has made his experiments to demonstrate that if the situation is very complex the line your aim with that you can get at various remarkable facts and I don't know if it's more realistic than the brain does something different what a timeline is just to suggest if it dipped artificial I'd like to think of it this way if there's an interpretation by some kind of objects under some of them anation then the brain thinks of them as common objects for instance as the sun goes down the

Sun one is getting much redder than a series. And yet the light the green the everything which the plants look green and they don't get ready is green and they don't change color illumination is changing and all the flowers in the garden aren't changing colors. If you take photographs with the film colored film of different illuminations and compare them you'll be surprised how different the actual light is that's coming to the eye in different situations of the sun. But you don't notice it anywhere nearly as great. Sometimes in the lady even you get a funny feeling at the something interesting about the light. Yes that's one it's extreme but you usually don't notice the differences and eliminate has a very great and it looks the same common Quite often that's when there's a different color being reflected off the clouds and it's coming from the sun also that he kept us this fetus and land has been able to reproduce this kind of an effect. Well not the effect of a funny feeling but the show as a demonstration he made in His father you take a board and place a lot of different colored papers are all different colors.

Browns greens pinks blue bright light bright ones dark once or colors. And there's one that looks white any illuminated with three focal lamps that we would talk about agreement in a blue and that's the only light that shines on in the room and you look at the new suit all the colors green are gluten and the white. He says now we're going to you look at any pick any spot you want like this bright this green paper. I'm going to rearrange the lamps so the light that comes from the White Paper is physically the same exactly as it came from the green paper before you see you can measure how much you know like the round the red lamp the brunette the green light and then you can adjust the knobs on the three layers so that the light the physical light measured by instruments that's coming from now from the white square is the same as coming from the Green Square before. Doesn't our green not at all. It's the most amazing you have to see it to believe it. It doesn't look any different at all. It looks exactly the same. You'd

swear he did nothing at all you just need to turn on the lights again as the white paper green papers are you can do with a brown spot. But even crazy take a place that looks brown and he adjusts the light from the white one to it would be the same as the ground of what look at it looks white again. In other words the eye sees the comparison of the different colors the relationship of the different colors and kind of corrects for the lighting if you will. What can't you think of as there are no conscious control no mind about this can't you tell yourself somehow when you know that this is a setup that you know the client has a different color and sort of regulate how those coasters are completely out of control. I haven't found myself able to control I think it's completely out of control must be some instinctive reaction that we aren't hearing the built in wired system for correcting for illumination a very useful thing. After all an animal has to recognize the same dog if it's known to be bug or if it's a food blog. All the time and respect about the illumination irrespective how far away it is and how close it is and whether the light is more yellow or less yellow is going to look like the same bot. So there's some

very early in evolution I'm sure this problem has been solved. Correcting for the lighting and we now have inherited from our earliest genetic ancestors the ability to see and interpret colors no matter what the light. Thank you thank you very much for being with us and telling us about color vision. This was about science with host Dr Albert Hibbs and his guest Dr Richard Feinman professor of physics at Cal Tech. Join us again for our next program when two more prominent scientists will discuss a subject of interest about science is produced by the California Institute of Technology and is originally broadcast by station KPCC in Pasadena California. The programs are made available to this station by national educational radio. This is the national educational radio network.