Light And Color (1961)

for [Music] [Applause] [Music] red paint green paint and blue paint you get a brownish mess but when you mix the same colors by eye you get a color that's very nearly White if you want to understand color you'll have to learn something about light because light and color are very closely related the sun is an excellent source of light and I can use this mirror to reflect some of that light onto the screen inside and there you see it appears to be white now here is a piece of clear plastic shaped like a triangle it's called a prism I'm going to use the prism so that a beam of the sun's white light passes through it and is reflected by the mirror onto the screen inside watch the light from the sun looks white but when this white light passes through this clear prism we see a spectrum of colors light and color seem to be connected so in order to learn about color first let's talk about light here is a panel with different shades of gray painted on it you can see the panel because the light is shining on it and some of the light is reflected back to your eyes but why do we see different parts of the panel as different Shades of Gray well the answer seems obvious enough it's because it's painted that way but that's not a good scientific answer to the question we still don't know exactly why the paints on this end look dark to us or why the paints on this end look light now here's a white card which I can make any shade of gray that you like watch this how did I do it easy I simply change the brightness of this light which shines on the white card by moving the light farther away when a lot of light shines on the card a lot of light is reflected back to your eye and the card looks white when less light shines on the card less is reflected back to your eye and the card looks gray let me show you we don't have to change the brightness of the light shining on the panel to see different Shades of Gray it's already painted that way but what about these paints why do some look darker to our eyes than others could it be that some paints reflect less light than others I can show you a piece of evidence to back up this this idea here are two aluminum frying pans let's paint one White and the other black and here lights both exactly alike and very powerful I'm going to shine one on the white frying pan and one on the black if what we've said is true the white pan is reflecting a lot of the light that hits it a lot of light is bouncing off of it back to our eyes and that's why it looks so bright the black pan isn't reflecting as much light and that's why it looks so dark but if it doesn't reflect the light that shines on it what does it do with it does it in some way soak up the light and the heat produced by the Light let's wait about 15 minutes and see after 15 minutes the two frying pans look the same as they did before but watch this the white pan reflected most of the light that has been beating down on it and so it hasn't gotten particularly hot although it would be warm if we touched it the black pan soaked up most of the light that hit it and as you can see the light has made it very hot now that's not a very efficient way to cook an egg but it does serve as a convincing piece of evidence it suggests that things that look dark to us look dark because they soak up or absorb more light than they reflect and the things that appear light appear that way because they reflect a great deal of light back to our eyes now we can talk about color you've already seen one piece of evidence suggesting that white light that is light such as you are looking at now and light from the sun are really made up of many different colors of light now let's see if we can mix colored lights together and make white light again here are three light projectors a red one a green one and a blue one now let's mix the three colors mixed together in this way the red green and blue lights look very nearly white so it seems that white light like this is really made up of light of different colors where's the red light coming from it's coming from here white light from the spotlight is hitting the card red light is being reflected off the card onto the boy's face the white light of the spotlight is made up of light of all colors including red there must be something about the red paint on this card that makes it able to reflect the red light and at the same time makes it soak up or absorb all the other colors besides red isn't it logical to think that the green paint on this card absorbs all the colors that make up the white light except green it reflects the green light the same with yellow and blue if what we have said is correct then the red part of this color wheel looks red to us because it absorbs all the colors that make up white light except red the red light is reflected back to our eyes the green part looks green because it reflects green light to our eyes and absorbs all the other colors and the blue part reflects blue light and absorbs the others too in white light we can see all the colors of the color wheel let's look at it now in green light look what happens when the color wheel is lit by green light only we see the green section of the color wheel clearly because the green section reflects green light back to our eyes but the red section and the blue section look almost black the red section and the blue section look dark because there is no red or blue light for them to reflect and they soak up the green light what do you think has happened now the green and blue sections are very dark but the red section is quite bright we have turned off the green light and turned on a red one what do you think will happen if we turn off the red light and turn on a blue one now the blue section is bright and the others are dark now you've had a chance to observe the effect of colored lights on colored objects perhaps the most important role that color plays in science has to do with a ATS each different kind of atom has a different set of colors no two sets are alike and so these sets of colors act kind of like fingerprints for atoms let me show you what I mean here are three small wire baskets each filled with a chemical if I light this gas jet notice it burns with the usual color but watch what happens when I heat up these chemicals sodium chloride turns the flame yellow cupric chloride turns it green and lithium chloride turns it red any material can be identified by its own unique colors this line Spectrum was made by heating up a chemical and sending a narrow beam of its light through a prism every different kind of material has a different set of these colors no two are alike astronomers are able to take light from Stars billions of miles away shine it through prisms and by using these color fingerprints discover what materials the Stars themselves are made up [Music] [Applause] [Music]