About science; About color vision

This is about a science produced by the California Institute of Technology and originally broadcast by station KPCC in Pasadena California. The programs are made available to this station by national education already. This program is about color vision with host Dr. Albert here 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 a 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 of the light that makes the color. But with all his 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 Calcutta act. 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. Wouldn't it be possible to get some understanding of color in terms of an analogy between sound and color between musical notes and different colors I got to back you up a bit. I back up that's when you hear people think and say that different colored cars by the different frequencies of light. But what's more complicated situation when you look at something to decide what the current of the thing is it doesn't depend so directly on the line that goes with 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. That is nearly always a red if it's pure but it's a in the green. It might look like life

might look like blue. It could look like brown that much different than yes it was a red like it would look like chocolate. OK well it aren't complicated I don't want to say that this guy can have these callers that they would go back a little bit and say Look prove my point of view. When you spread the light out of different kinds of light physically different kinds of light and your analogy is a good one will college buy into like high note that blue end of the spectrum and the other kinds bundle low notes like the red and the what we call the red and white. But in the other very interesting other good enough to do with mixing. Suppose that I shine if they place two bits of spectrum light. OK I'll buy it too differently. That would correspond to having in the year at the same time two notes being played in the piano simultaneously in the year you hear these two distinct know as to not have to know 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 from the whole you know well you can't tell it what the two were that went together to make that call. Like in the year you could still hear if you're clever or they tell me my ears and so good they tell me that you can still make out the individual not. But even worse let me go. It turned out to bear the weight of the I can't have a dialogue and explain it in this way I can take distributions of life like I take some from one part of the spectrum and some of the other and some other mix them together like a painter making Thanks to let me just mix the lights will come to what I paid but very much like a play to make this place but you're not making bank money thing like I'm shining like a different kind a life together than I get some kind of an effect on the eye. Now I don't doubt there may be another mixture of completely different bits of the spectrum might be you mix together in a certain proportion that is absolutely

indistinguishable by the I the thing that would happen in a year would be that someone would play three notes on a piano and then by pushing around on the scale find three other notes say for instance that he could play that you couldn't count was different than the first. We didn't play and that doesn't happen now that happened but it does with the ear can analyze it with far more that much closer to the detailed physical property than I can tell the eye and seem like. It cannot distinguish all of the details of the way that light is physically for there are many different ways of physically for me alike that look exactly the same to the 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 color yet isn't well if you're going to reply to speculate. Red Green Blue by that put some kind of way of shining just a bit of the red blood as we I should say boy exactly one wavelength of the spectrum with

another way in another way and I adjust the amount of the green and I can image that anything they see any light of any kind. It's made by mixing any other girl like 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 Sattar there are some rules about what particular kind you can cause if you're one of the inspector many that there's some complication we complicate I want to make a proposition for him and again we get to the company. Let's take a definite set of 3 8 doesn't make it work if you put your reply to the victim. They were near the red and the green in the right. OK and you let the light from each of the sections through but please look at a screen all over like I think you know in just the way you have adjustment that you can put different report like a colored glass in front of like something like that that you could also do it just as well.

What I'm talking about I think three lamps that bring a piece of glass are threaded but I want to be the glasses Green beat a glass of blue with one another and that's one way to adjust the brightness of the lamp and shine only three lights on the same right now you could make any other light like a railroad man signal lamp or something and shine it I can imitate the light of the railroad man single I have exactly so that the eye can see your I can't see the difference in that light by adjusting the amount of the three the red green and the blue one. Some kind I might need a negative amount of one of the lights in order that it may not Maggie back with so it sucks light out and might be a little hard to accomplish. Can you explain what you mean by and yet ignored amount like if you took I suppose that when I want to imitate is a very move like you say for example. OK and the blue and I happen to be using is more close to the green than my blue in my green can make it only in the greenish blue region and adding red isn't going to make it blue and it makes a yellow dot and it

makes it work. I'm trying in a table then I can get that with the blues and greens for instance. But if I would like to suck some right out or print I might take some blue and suck some green out the best way to do it way I might be able to with the pick the green lamp 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 resolve I can mix it with blue and red. It's like putting it on the other side of the equation. It's better to say x is equal a certain amount of red but a certain amount of green for that amount of will 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 color. And a tree light with one minor exception.

If one of the lights could be imitated by mixing the other to the end that you don't have anything so you have three like that it's going to be this big. Let me go back a minute to something I mentioned just a little earlier about the mixing of paint and he said that isn't what you're talking about what's the difference between making from the primary color of paint making a like you know you're not now and I do like that we're talking about a light that we see see what we see the stuff that comes into the eye now how it got that way depending upon what happened to it on the way. For example the light that comes into the eye is not the light of the sun on my up I was the light of the sun modified by the colored pigments in the leaf in particular like my little red of the short wavelength and the long way like it was like a lot of the other. And and so it appears a different color a light that we can the eye is different than the light of the sun now. Pigment

paper and dyes and so on. I 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 right so when you mix paint is quite a different thing and mixing light because when for example suppose you take a blue and yellow pigment as every child knows you get green right. Makes you right. But if you take blue and yellow light and shine it together on a place it looks like white light green glow green look at all I can say really something quite different quite frankly in lights out of colored light bulbs and there is a lot of mixing things. Yes the reason is that yellow paper. It's a pain which takes out the red end of the spectrum and leaves the Greens and the blues and everything together and it looks yellow yellow and green and blues.

Now a blue paint is something that takes out the yellow and the red of the spectrum and just leave the bluish and greenish part of the spectrum come to your eye if you mix the both plates or let's say easy and likely both they'd imagine two pieces of cellophane one and thought of the other one which is agreeable which is one which is blue A which is yellow yellow one let's throw everything but red the blue one on top of that will let through would take away the yellow part of the spectrum and leave just the green the green in the blue it has an excess of green though is a different kind of proportion it's not like adding it's picking away. I think one of the techniques show yet again is takeout because of the spectrum because they don't like it I don't let it rule where and when I put in the lights to get I'm adding that to like I'm letting both can wear the other way I double subtraction sort of like pick 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 it doesn't work out anymore because you know that it is at a regime when you do it with thinking. That's right and that if I were to see another interesting effect which I should mention because otherwise you get

confused a bit like an out-of-body a life review and there's a following. I said that we could imitate two lights exactly. By mixing They say at one any old 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 who lights if they enter the eye would be identical but they shine on a piece of some like a green leaf. You could tell the difference. Because belief takes out different amounts of different parts of the spectrum for example it takes out some of the red say so. Since my Vista beauticians although they appear to the eye the thing after I take out the red They don't let go of the idea. I only started with red only you'd get a different thing when you just cut down the red berry like Iraq agree after 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 there are things which look the same to be are I because they have a certain distribution of a lot of the different colored

lights that distributions will be changed in a different way by the door that light the green so that to cut through things light would look with a lot of white paper will not produce equivalent will not necessary look at equivalent when reflected from a colored piece of paper. Are there different or at least had to do nothing with the eye. What about the oh it has to do with thing we can figure out it had to do with how the light bounces from all the objects as well. Physics is easy to figure out a completely definite The figure out of any sort. That's exactly what this division of all the parts of the spectrum is coming into the on the interesting question then is. Forget the physical how it got to the night when it's gotten to the eye and you know what's coming into the ice what determine right happen are why they're never going to different cells respond to each different color it was not exactly known. Simplest theory which explains these businesses about mixing colors is that there are three different kinds of cells that had three different kind of pigments in them let me explain how it might work.

First it was colorblind. OK so then with the that there was a colored so I suppose that you had a beam in the eye as a self innocent chemical cell and were like gigantic chemical changes that can. When a chemical Jane nerve impulses go off that's not necessarily exactly the way it goes but the view from which you can understand everything is gone now so that narrative only can know how much chemical has been converted. It doesn't know anything else about the light except what the light did namely to up this chemical and make a new guy in the field right. But different colored different parts of the spectrum may be an equally effective like bird. Let's suppose that red light doesn't look like the chemical little red end of the spectrum and the yellow and the blue and the like it pretty well and the yellow and green and buy the thing affected pretty well but the blue doesn't effect very well for example that 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 being transformed if we used then a little green light we can transform the same amount of chemical. Go a little bit of green would look exactly the same as over a lot of rain with that particular sound that they get us out but all not being seas 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 very crude it in the sense that this music with no noise it would know the picture is the same way with no light but it doesn't know the color. It's more sensitive to one kind of light and they were not. But it was only like OK now I want you to imagine and notice all of that place that the color blind eye has only one kind of pigment which we place a green sensitive not as the right. Now

suppose that this guy or others with a different pigment and I suppose but definite understand it this big is sensitive in a red red light and not very sensitive with Partly said the green is not said to the blue say OK so now you are one tell exactly the green Are you brought in one of the companies direct That's right. They both work pretty much with the same mechanism but one do it for the red like me other for the grants right now we want to know can the brain get any clue as to the character of the color of the light and I should think so by comparing the output of the two cells in your mouth. Right because a green light. Will affect one album not the OT it will affect say the first one I mean you will call a unicycle and be will greenlight make 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 might just like to be married more so that brains are as big as the information available to him as possible but to figure out that there's a different character in the light when you

shine a red when you shine a green physical light if you shine right now in between which might affect both of the two pigment equally. For example then the thing will go up equally right. Now you notice that that can't be distinguished from a combination of red and green. A combination who likes red physical and green politically because it affects both pigment Bickley and both light shining on the brain with would do the same thing and therefore a light which is in the middle of the spectrum yob would be physically I mean optically a physiological beyond exactly to say that a mixture of red and green. And that's what we find we find that we can imitate life we just read and so the guess is we have three different thing with two letters as an extra. The idea is the same as just one more. Why do we need three How about taking the opposite ends of the spectrum Violet in a red wooden different proportions of those to make everything in between.

We couldn't distinguish you see but you could 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 length and a light that's green in the middle like to tell you it 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 situations in the world which the eye can't distinguish namely that from the flower is being reflected in equal amount of red light and blue light warm from the flowers 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 insensitivity in the middle or third bigmouth in this thing which a little more for peanuts we would have a greater range of color understanding in the sense that things that were physically not the same would be just the thing I was able to see if we had a million of them and we had him much like

he would be likely or again it would be you are alone here and you see a lot of wonderful the way that we may encounter. Well if a color photograph is made then it is not necessary to use in a color photograph any particular set of pigments that use another sentence to reproduce the scene. Rather like that roughly speaking because you can get every proportion of the different color like human by having different color pigments mixed up in the photographic plate. The trouble is that the minus numbers as I told you. Theoretically we 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 a third of the way to do that. And therefore if you use certain particular dies you get a greater range of possible colors without using a negative side than if you have another grain or some special combination of works for that. Yes but I now know were at a wider range of what's the best to depend on which one of the most direct you were born you gonna lose. We're losing some sense at least only it's hard to count how many.

There's no I don't want what you want anyway. And then an actual car business that the technical problems of which dies are read the word photographically and so on and so there are various compromises made you know good even the best ideals or why is it want to. You're in a room that has just slightly orange light already light like an incandescent light bulb would certainly have yellow or redder than sunlight. Things to look the same car very nearly. That's a very remarkable thing that's important. I mean that was likely true it's very true it is very important to the distinction understand distinction between a light which reaches the eye and the current sensation that we see. Remember I said that with a reddish light you might see. Let me give an example how about if like you would be OK if you have a circle a document absolutely daku and the only thing a light is coming from is some circle. And it's a red light. It looks nice in bed in the dark.

OK but if you will now have another ring outside of the red circle like the packages you sent it exactly the same as it was before with the same light coming from the Red Bull the red bull's eye no red light coming from the bull's eye to look at out of a painted wall I know it's a spot that light is coming I don't know how it came but it's coming from the bull's eye that a red line and around that we have already se wide raid in which a white light say there are many combinations of this phenomenon but it will take white light is coming that if the white light is much stronger than the red light it looked like a clock with the central spot you see what Brown is is a place that isn't as bright as its neighborhood around it. Hand out the collar of the different kinds of brows had to do with a character like that coming in are you sure is a different type of brown the other rider ID of a different beautiful bride that comes from having different colored lights but the character that makes it

Brown had to do with the general illumination and background you know that that's a relatively dark area but some color some light is coming compared to the surroundings so there's not not an absolute then I don't have any brightness it always compared to what is going on it looks like they're arguing exactly and it's this sensation that we get from light from from looking is not just dependent on the light but how that light is developed at the neighborhood. So if I just turned on the lights in a room that has that has a something red on the wall won't turn brown because everything else is down because that's a good example. That's right exactly I mean in the light bridges but not from a wall you know ordinary lives if you could just keep that isolate take it away don't like and surround it by a much brighter white light it would look dark. That of that of ours to get the greenish yellow

lab release your life a little bit of white background scar that I didn't get that sort of dirty greenish color like the Army uniform carrying Well how is it is it not possible 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 allays like completely red or some such they have not got a wide distribution of colors in it. If I just change from one color like to another and I was in a room I wanted to thank you a lot in that moment when you're jaded but if the light is light very severely colored. GRAMLICH scream that it will be still be the full range of colors even though it hangs like it shining on it. I visited a land that was landed at the power company. He's the one who wrote an article of after some trying to figure Merican is going to run 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 do experiments in psychology or theory they add artificial situations a very simple like a circle of circles. Yeah yeah and they have noticed the number of the effects that I just talked about that the light that the colors look depend upon the Rev.. Well it turned out that a real situation or a complicated situation the effects are enormously more powerful that it had been realized before actually and he has made his experiment to demonstrate that the situation is very complex. The lie you are a with that you can get a very remarkable effect and I don't know if it's more realistic than the brain does something different what I want you to guess. If it if the artificial I don't like to think of it this way if there's an interpretation like some kind of objects under some illumination then the brain thinks of them as colored objects. Reduces as the sun goes down.

The sunlight is getting much redder every series and yet the light there every day with the plants look green and they don't get ready is green and they don't change color the illuminations changing at all like I was a God now and changing color. If you take a photograph with a film colored girl at 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 anyway nearly as great. Sometimes in the late even you get a funny feeling that there's something that interesting about the light yet that's when it's extreme but you usually don't notice the differences really eliminate has a very great and it looks the same coming quite often that's when there's a different color being reflected off the clouds and that's coming from a Sun offer that you get that this feeling of land land has been able to reproduce this kind of an effect. Well not be a regular funny feeling but the show as a demonstration he made famous by the board and paid a lot of different colored papers all different. BROWN The

Greens pink blue bright light bright was dark woods or cold and there's one that looks white and me illuminated with creepy local lamps that we would talk about right I would agree with that a blogger only like that you and I will. You got it when you see all the colors green on blue killings and the like. He says now we are going through. You look at any pick any bike you want like this bright this green paper. I'm going to rearrange the lamps so the light that comes with the white paper is physically the same exactly as it came from the green paper before you can measure how much. Yeah like that I'm a red lamp the brunette agreement with anything or just a lot of Leave It To The Light of physical life led by instruments that's coming from now from the white square is the same as coming from the Green Square before to the now agreeing not at all. It's the most amazing you have to see it to believe it doesn't look any different at

all. It looks exactly the same. You'd swear he did nothing. Only if you're going to turn on a light to get there. The white paper green things you can do with a brown spot. But even Grady take a place that looks brown and he adjusts the light from the White with the oil would be the same with the ground or what look at it looks white again. In other words the ice sees the comparison of the different colors the relationship of the different colors and kind of corrects for the lighting if you will. Do you think about is there no conscious control no mind about it can't you tell yourself somehow when you know that this is a setup that you know that light is a different color and sort of regulate how those builders are completely out of control. I haven't I saw they were control I think it's completely out of control must be some instinctive reaction that we are hearing. Bill did a wired system for correcting for illumination a very useful thing draw an animal after recognizes a bug particularly buggle it as a food blog or with a title and respective of the illumination irrespective how far away it is and I'll close it

is of whether the light is more yellow or less yellow is going to look like the same box. So there's some very early in evolution I'm sure the problem with a little sob of 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 like. Rick Decker thank you very much for being with us and telling us about color vision. This was about science with host Dr. Albert hid and he's against Dr Richard Feinman professor of physics at Cal Tech. Join us again for our next program when two more prominent scientists. Well that's got a subject of interest about science is produced by the California Institute of Technology and is originally broadcast by station PPC Pasadena California. The programmes are made available to this station by national educational radio. This is the national educational radio network.