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reflective qualities of paint colors
Posted by Frank Canna
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Re: reflective qualities of paint colors December 13, 2006 03:12AM |
[www.physicsclassroom.com]
Lesson 2: Color and Vision
Light Absorption, Reflection, and Transmission
We have previously learned that visible light waves consists of a continuous range of wavelengths or frequencies. When a light wave with a single frequency strikes an object, a number of things could happen. The light wave could be absorbed by the object, in which case its energy is converted to heat; the light wave could be reflected by the object; and the light wave could be transmitted by the object. Rarely however does just a single frequency of light strike an object. While it does happen, it is more usual that light of many frequencies or even all frequencies are incident towards the surface of objects. When this occurs, objects have a tendency to selectively absorb, reflect or transmit light of certain frequencies. That is, one object might reflect green light while absorbing all other frequencies of visible light. Another object might selectively transmit blue light while absorbing all other frequencies of visible light. The manner in which visible light interacts with an object is dependent upon the frequency of the light and the nature of the atoms of the object. In this section of Lesson 2 we will discuss how and why light of certain frequencies can be selectively absorbed, reflected or transmitted.
Atoms and molecules contain electrons. It is often useful to think of these electrons as being attached to the atoms by springs. The electrons and their attached springs have a tendency to vibrate at specific frequencies. Similar to a tuning fork or even a musical instrument, the electrons of atoms have a natural frequency at which they tend to vibrate. When a light wave with that same natural frequency impinges upon an atom, then the electrons of that atom will be set into vibrational motion. (This is merely another example of the resonance principle introduced in Unit 11 of The Physics Classroom.) If a light wave of a given frequency strikes a material with electrons having the same vibrational frequencies, then those electrons will absorb the energy of the light wave and transform it into vibrational motion. During its vibrations, the electrons interacts with neighboring atoms in such a manner as to convert its vibrational energy into thermal energy. Subsequently, the light wave with that given frequency is absorbed by the object, never again to be released in the form of light. So the selective absorption of light by a particular material occurs because the selected frequency of the light wave matches the frequency at which electrons in the atoms of that material vibrate. Since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies of visible light.
Reflection and transmission of light waves occur because the frequencies of the light waves do not match the natural frequencies of vibration of the objects. When light of these frequencies strike an object, the electrons in the atoms of the object begin vibrating. But instead of vibrating in resonance at a large amplitude, the electrons vibrate for brief periods of time with small amplitudes of vibration; then the energy is reemitted as a light wave. If the object is transparent, then the vibrations of the electrons are passed on to neighboring atoms through the bulk of the material and reemitted on the opposite side of the object. Such frequencies of light waves are said to be transmitted. If the object is opaque, then the vibrations of the electrons are not passed from atom to atom through the bulk of the material; rather the electrons vibrate for short periods of time and then reemit the energy as a reflected light wave. Such frequencies of light are said to be reflected.
The color of the objects which we see are largely due to the way those objects interact with light and ultimately reflect or transmit it to our eyes. The color of an object is not actually within the object itself; rather, the color is in the light which shines upon it that ultimately becomes reflected or transmitted to our eyes. We know that the visible light spectrum consists of a range of frequencies, each of which corresponds to a specific color. When visible light strikes an object and a specific frequency becomes absorbed, that frequency of light will never make it to our eyes. Any visible light which strikes the object and becomes reflected or transmitted to our eyes will contribute to the color appearance of that object. So the color is not in the object itself, but in the light which strikes the object. The only role that the object plays is that it might contain atoms capable of absorbing one or more frequencies of the visible light which shine upon it. So if an object absorbs all of the frequencies of visible light except for the frequency associated with green light, then the object will appear green in the presence of ROYGBIV. And if an object absorbs all of the frequencies of visible light except for the frequency associated with blue light, then the object will appear blue in the presence of ROYGBIV.
Consider the two diagrams below. The diagrams depict a sheet of paper being illuminated with white light (ROYGBIV). The papers are impregnated with a chemical capable of absorbing one or more of the colors of white light. Such chemicals which are capable of selectively absorbing one or more frequency of white light is known as a pigment. In Example A, the pigment in the sheet of paper is capable of absorbing red, orange, yellow, green, indigo and violet. In Example B, the pigment in the sheet of paper is capable of absorbing orange, yellow, green, blue, indigo and violet. In each case, whatever color is not absorbed is reflected. Check your understanding of these principles by determining which color(s) of light are reflected by the paper and what color the paper will appear to an observer.
Depress mouse to view answer.Example A: Green will be reflected andso the paper appears green to anobserver.Example B: Red will be reflected andso the paper appears red to anobserver.
Transparent materials are materials which allow one or more of the frequencies of visible light to be transmitted through them; whatever color(s) is/are not transmitted by such objects, are typically absorbed by them. The appearance of a transparent object is dependent upon what color(s) of light is/are incident upon the object and what color(s) of light is/are transmitted through the object. Express your understanding of this principle by filling in the blanks in the following diagrams.
Depress mouse to view answer.Example A: Green will be transmittedand so the object appears green to anobserver.Example B: Both green and blue will betransmitted and so the object appearsgreenins-blue to an observer.
The colors perceived of objects are the results of interactions between the various frequencies of visible light waves and the atoms of the materials which objects are made of. Many objects contains atoms capable of either selectively absorbing, reflecting or transmitting one or more frequencies of light. The frequencies of light which become transmitted or reflected to our eyes will contribute to the color which we perceive.
Check Your Understanding
1. Natural philosophers have long pondered the underlying reasons for color in nature. One common historical belief was that colored objects in nature produce small particles (perhaps light particles) which subsequently reach our eyes. Different objects produce different colored particles, thus contributing to their different appearance. Is this belief accurate or not? Justify your answer.
Depress mouse to view answers.This view is not accurate and presumes that theappearance of an object is independent of thecolors of light which illuminate the object.We observe that the same object appearsdifferent colors when viewed under different light.So the secret to an object's appearance is notstrictly due to its ability to produce a color.In fact the object's only role in determining itsappearance is in its ability to absorb certainwavelengths of light which shine upon it.
2. What color does a red shirt appear when the room lights are turned off and the room is entirely dark? ____________ What about a blue shirt? ____________ ... a green shirt? ____________
Depress mouse to view answers.Answer: BlackWhen the room lights are turned off (there isno light), any object present in the room appearsblack. The color appearance of an object dependsupon the light which that objects reflects tothe observer's eye. Without any incident light,there can be no reflected light. Such an objectappears black - the absence of light.
3. The diagrams depict a sheet of paper being illuminated with white light (ROYGBIV). The papers are impregnated with a chemical capable of absorbing one or more of the colors of white light. In each case, determine which color(s) of light are reflected by the paper and what color the paper will appear to an observer.
Depress mouse to view answer.Practice A: No light will be reflected;it is all absorbed. Thus, the paperwould appear black to an observer.Practice B: Red and orange will bereflected and so the paper appearsreddish-orange to an observer.
4. The appearance of a transparent object is dependent upon what color(s) of light is/are incident upon the object and what color(s) of light is/are transmitted through the object. Express your understanding of this principle by determining which color(s) of light will be transmitted and what color which the paper will appear to an observer.
Depress mouse to view answer.Practice A: Green and blue lightwill be transmitted and so the objectwould appear greenish-blue to anobserver.Practice B: Red and orange lightwill be transmitted and so the objectwould appear reddish-orange to anobserver.
Depress mouse to view answer.Practice A: Red and blue lightwill be transmitted and so the objectwould appear reddish-blue to anobserver.Practice B: Only red light will betransmitted and so the objectwould appear red to an observer.
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NEXT >>
Color Addition
Color perception, like sound perception, is a complex subject involving the disciplines of psychology, physiology, biology, chemistry and physics. When you look at an object and perceive a distinct color, you are not necessarily seeing a single frequency of light. Consider for instance that you are looking at a shirt and it appears purple to your eye. In such an instance, there my be several frequencies of light striking your eye with varying degrees of intensity; yet your eye-brain system interprets the frequencies which strike your eye and the shirt is decoded as being "purple."
The complexities of color perception can be reduced if we think in terms of primary colors of light. We have already learned that white is not a color at all, but rather the presence of all the frequencies of visible light. When we speak of white light, we are referring to ROYGBIV - the presence of the entire spectrum of visible light. But combining the range of frequencies in the visible light spectrum is not the only means of producing white light. White light can also be produced by combining only three distinct frequencies of light, provided that they are widely separated on the visible light spectrum. Any three colors (or frequencies) of light which produce white light when combined with the correct intensity are called primary colors of light. There are a variety of sets of primary colors; yet,the most common set of primary colors is red (R), green (G) and blue (
. When red, green and blue light are mixed or added together with the proper intensity, white (W) light is obtained. This is often represented by the equation below:
R + G + B = W
In fact, the mixing together (or addition) of these three primary colors of light with varying degrees of intensity can produce a wide range of other colors. For this reason, television sets and computer monitors produce the range of colors on the monitor by the use of of red, green and blue phosphors.
The addition of the primary colors of light was demonstrated in class using a light box. The light box illuminated a screen with the primary colors red (R), green (G) and blue (; the lights were the shape of circles. The result of adding two primary colors of light was easily seen by viewing the overlap of the two or more circles of primary light. The different combinations of colors produced by red, green and blue are shown in the graphic below. (CAUTION: Because of the way that different monitors and different web browsers render the colors on the computer monitor, there may be slight variations from the intended colors.)
These demonstrations with the color box illustrated that red light and green light add together to produce yellow (Y) light; red light and blue light add together to produce magenta (M) light; green light and blue light add together to produce cyan (C) light; and finally, red light and green light and blue light add together to produce white light. This is sometimes demonstrated by the following equations and graphic:
R + G = Y
R + B = M
G + B = C
Yellow (Y), magenta (M) and cyan (C) are sometimes referred to as secondary colors of light since they are produced by the addition of equal intensities of two primary colors of light. The addition of these three primary colors of light with varying degrees of intensity will result in the other colors found in the visible light spectrum.
Any two colors of light which produce white are said to be complementary colors of each other. The complementary color of red light is cyan light. This is reasonable since cyan light is the combination of blue and green light; and blue and green light when added to red light will produce white light. Thus, red light and cyan light (blue + green) represent a pair of complementary colors; they add together to produce white light. This is illustrated in equation form below:
R + C = R + (B + G) = White
Each primary color of light has a secondary color of light as its complement. The three pairs of complementary colors are listed below. The graphic is extremely helpful in identifying complementary colors. Complementary colors are always located directly across from each other on the graphic. Note that cyan is located across from red, magenta across from green, and yellow across from blue.
Complementary Colors of Light
Red and Cyan
Green and Magenta
Blue and Yellow
The production of various colors of light by the mixing of the three primary colors of light is known as color addition. The color addition principles discussed on this page can be used to make predictions of the colors which would result when different colored lights are mixed. In the next part of Lesson 2, we will learn how to use the principles of color addition to determine why different objects look specific colors when illuminated with various colors of light.
Check Your Understanding
1. Two lights are arranged above a white sheet of paper. When the lights are turned on they illuminate the entire sheet of paper (as seen in the diagram below). Each light bulb emits a primary color of light - red (R), green (G), and blue (. Depending on which primary color of light is used, the paper will appear a different color. Express your understanding of color addition by determining the color which the sheet of paper will appear in the diagrams below.
Depress mouse to view answer.R + G ---> YellowR + B ---> MagentaB + G ---> Cyan
2. If magenta light and yellow light are added together, will white light be produced? Explain.
Depress mouse to view answer.No. Magenta is a combination of redand blue light and yellow is acombination of red and green light.(Note the double abundance of red.)Combining magenta and yellow willproduce a whitish-red color - thatis, pink.
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CONTINUED...
Lesson 2: Color and Vision
Light Absorption, Reflection, and Transmission
We have previously learned that visible light waves consists of a continuous range of wavelengths or frequencies. When a light wave with a single frequency strikes an object, a number of things could happen. The light wave could be absorbed by the object, in which case its energy is converted to heat; the light wave could be reflected by the object; and the light wave could be transmitted by the object. Rarely however does just a single frequency of light strike an object. While it does happen, it is more usual that light of many frequencies or even all frequencies are incident towards the surface of objects. When this occurs, objects have a tendency to selectively absorb, reflect or transmit light of certain frequencies. That is, one object might reflect green light while absorbing all other frequencies of visible light. Another object might selectively transmit blue light while absorbing all other frequencies of visible light. The manner in which visible light interacts with an object is dependent upon the frequency of the light and the nature of the atoms of the object. In this section of Lesson 2 we will discuss how and why light of certain frequencies can be selectively absorbed, reflected or transmitted.
Atoms and molecules contain electrons. It is often useful to think of these electrons as being attached to the atoms by springs. The electrons and their attached springs have a tendency to vibrate at specific frequencies. Similar to a tuning fork or even a musical instrument, the electrons of atoms have a natural frequency at which they tend to vibrate. When a light wave with that same natural frequency impinges upon an atom, then the electrons of that atom will be set into vibrational motion. (This is merely another example of the resonance principle introduced in Unit 11 of The Physics Classroom.) If a light wave of a given frequency strikes a material with electrons having the same vibrational frequencies, then those electrons will absorb the energy of the light wave and transform it into vibrational motion. During its vibrations, the electrons interacts with neighboring atoms in such a manner as to convert its vibrational energy into thermal energy. Subsequently, the light wave with that given frequency is absorbed by the object, never again to be released in the form of light. So the selective absorption of light by a particular material occurs because the selected frequency of the light wave matches the frequency at which electrons in the atoms of that material vibrate. Since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies of visible light.
Reflection and transmission of light waves occur because the frequencies of the light waves do not match the natural frequencies of vibration of the objects. When light of these frequencies strike an object, the electrons in the atoms of the object begin vibrating. But instead of vibrating in resonance at a large amplitude, the electrons vibrate for brief periods of time with small amplitudes of vibration; then the energy is reemitted as a light wave. If the object is transparent, then the vibrations of the electrons are passed on to neighboring atoms through the bulk of the material and reemitted on the opposite side of the object. Such frequencies of light waves are said to be transmitted. If the object is opaque, then the vibrations of the electrons are not passed from atom to atom through the bulk of the material; rather the electrons vibrate for short periods of time and then reemit the energy as a reflected light wave. Such frequencies of light are said to be reflected.
The color of the objects which we see are largely due to the way those objects interact with light and ultimately reflect or transmit it to our eyes. The color of an object is not actually within the object itself; rather, the color is in the light which shines upon it that ultimately becomes reflected or transmitted to our eyes. We know that the visible light spectrum consists of a range of frequencies, each of which corresponds to a specific color. When visible light strikes an object and a specific frequency becomes absorbed, that frequency of light will never make it to our eyes. Any visible light which strikes the object and becomes reflected or transmitted to our eyes will contribute to the color appearance of that object. So the color is not in the object itself, but in the light which strikes the object. The only role that the object plays is that it might contain atoms capable of absorbing one or more frequencies of the visible light which shine upon it. So if an object absorbs all of the frequencies of visible light except for the frequency associated with green light, then the object will appear green in the presence of ROYGBIV. And if an object absorbs all of the frequencies of visible light except for the frequency associated with blue light, then the object will appear blue in the presence of ROYGBIV.
Consider the two diagrams below. The diagrams depict a sheet of paper being illuminated with white light (ROYGBIV). The papers are impregnated with a chemical capable of absorbing one or more of the colors of white light. Such chemicals which are capable of selectively absorbing one or more frequency of white light is known as a pigment. In Example A, the pigment in the sheet of paper is capable of absorbing red, orange, yellow, green, indigo and violet. In Example B, the pigment in the sheet of paper is capable of absorbing orange, yellow, green, blue, indigo and violet. In each case, whatever color is not absorbed is reflected. Check your understanding of these principles by determining which color(s) of light are reflected by the paper and what color the paper will appear to an observer.
Depress mouse to view answer.Example A: Green will be reflected andso the paper appears green to anobserver.Example B: Red will be reflected andso the paper appears red to anobserver.
Transparent materials are materials which allow one or more of the frequencies of visible light to be transmitted through them; whatever color(s) is/are not transmitted by such objects, are typically absorbed by them. The appearance of a transparent object is dependent upon what color(s) of light is/are incident upon the object and what color(s) of light is/are transmitted through the object. Express your understanding of this principle by filling in the blanks in the following diagrams.
Depress mouse to view answer.Example A: Green will be transmittedand so the object appears green to anobserver.Example B: Both green and blue will betransmitted and so the object appearsgreenins-blue to an observer.
The colors perceived of objects are the results of interactions between the various frequencies of visible light waves and the atoms of the materials which objects are made of. Many objects contains atoms capable of either selectively absorbing, reflecting or transmitting one or more frequencies of light. The frequencies of light which become transmitted or reflected to our eyes will contribute to the color which we perceive.
Check Your Understanding
1. Natural philosophers have long pondered the underlying reasons for color in nature. One common historical belief was that colored objects in nature produce small particles (perhaps light particles) which subsequently reach our eyes. Different objects produce different colored particles, thus contributing to their different appearance. Is this belief accurate or not? Justify your answer.
Depress mouse to view answers.This view is not accurate and presumes that theappearance of an object is independent of thecolors of light which illuminate the object.We observe that the same object appearsdifferent colors when viewed under different light.So the secret to an object's appearance is notstrictly due to its ability to produce a color.In fact the object's only role in determining itsappearance is in its ability to absorb certainwavelengths of light which shine upon it.
2. What color does a red shirt appear when the room lights are turned off and the room is entirely dark? ____________ What about a blue shirt? ____________ ... a green shirt? ____________
Depress mouse to view answers.Answer: BlackWhen the room lights are turned off (there isno light), any object present in the room appearsblack. The color appearance of an object dependsupon the light which that objects reflects tothe observer's eye. Without any incident light,there can be no reflected light. Such an objectappears black - the absence of light.
3. The diagrams depict a sheet of paper being illuminated with white light (ROYGBIV). The papers are impregnated with a chemical capable of absorbing one or more of the colors of white light. In each case, determine which color(s) of light are reflected by the paper and what color the paper will appear to an observer.
Depress mouse to view answer.Practice A: No light will be reflected;it is all absorbed. Thus, the paperwould appear black to an observer.Practice B: Red and orange will bereflected and so the paper appearsreddish-orange to an observer.
4. The appearance of a transparent object is dependent upon what color(s) of light is/are incident upon the object and what color(s) of light is/are transmitted through the object. Express your understanding of this principle by determining which color(s) of light will be transmitted and what color which the paper will appear to an observer.
Depress mouse to view answer.Practice A: Green and blue lightwill be transmitted and so the objectwould appear greenish-blue to anobserver.Practice B: Red and orange lightwill be transmitted and so the objectwould appear reddish-orange to anobserver.
Depress mouse to view answer.Practice A: Red and blue lightwill be transmitted and so the objectwould appear reddish-blue to anobserver.Practice B: Only red light will betransmitted and so the objectwould appear red to an observer.
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NEXT >>
Color Addition
Color perception, like sound perception, is a complex subject involving the disciplines of psychology, physiology, biology, chemistry and physics. When you look at an object and perceive a distinct color, you are not necessarily seeing a single frequency of light. Consider for instance that you are looking at a shirt and it appears purple to your eye. In such an instance, there my be several frequencies of light striking your eye with varying degrees of intensity; yet your eye-brain system interprets the frequencies which strike your eye and the shirt is decoded as being "purple."
The complexities of color perception can be reduced if we think in terms of primary colors of light. We have already learned that white is not a color at all, but rather the presence of all the frequencies of visible light. When we speak of white light, we are referring to ROYGBIV - the presence of the entire spectrum of visible light. But combining the range of frequencies in the visible light spectrum is not the only means of producing white light. White light can also be produced by combining only three distinct frequencies of light, provided that they are widely separated on the visible light spectrum. Any three colors (or frequencies) of light which produce white light when combined with the correct intensity are called primary colors of light. There are a variety of sets of primary colors; yet,the most common set of primary colors is red (R), green (G) and blue (
. When red, green and blue light are mixed or added together with the proper intensity, white (W) light is obtained. This is often represented by the equation below:
R + G + B = W
In fact, the mixing together (or addition) of these three primary colors of light with varying degrees of intensity can produce a wide range of other colors. For this reason, television sets and computer monitors produce the range of colors on the monitor by the use of of red, green and blue phosphors.
The addition of the primary colors of light was demonstrated in class using a light box. The light box illuminated a screen with the primary colors red (R), green (G) and blue (
; the lights were the shape of circles. The result of adding two primary colors of light was easily seen by viewing the overlap of the two or more circles of primary light. The different combinations of colors produced by red, green and blue are shown in the graphic below. (CAUTION: Because of the way that different monitors and different web browsers render the colors on the computer monitor, there may be slight variations from the intended colors.)
These demonstrations with the color box illustrated that red light and green light add together to produce yellow (Y) light; red light and blue light add together to produce magenta (M) light; green light and blue light add together to produce cyan (C) light; and finally, red light and green light and blue light add together to produce white light. This is sometimes demonstrated by the following equations and graphic:
R + G = Y
R + B = M
G + B = C
Yellow (Y), magenta (M) and cyan (C) are sometimes referred to as secondary colors of light since they are produced by the addition of equal intensities of two primary colors of light. The addition of these three primary colors of light with varying degrees of intensity will result in the other colors found in the visible light spectrum.
Any two colors of light which produce white are said to be complementary colors of each other. The complementary color of red light is cyan light. This is reasonable since cyan light is the combination of blue and green light; and blue and green light when added to red light will produce white light. Thus, red light and cyan light (blue + green) represent a pair of complementary colors; they add together to produce white light. This is illustrated in equation form below:
R + C = R + (B + G) = White
Each primary color of light has a secondary color of light as its complement. The three pairs of complementary colors are listed below. The graphic is extremely helpful in identifying complementary colors. Complementary colors are always located directly across from each other on the graphic. Note that cyan is located across from red, magenta across from green, and yellow across from blue.
Complementary Colors of Light
Red and Cyan
Green and Magenta
Blue and Yellow
The production of various colors of light by the mixing of the three primary colors of light is known as color addition. The color addition principles discussed on this page can be used to make predictions of the colors which would result when different colored lights are mixed. In the next part of Lesson 2, we will learn how to use the principles of color addition to determine why different objects look specific colors when illuminated with various colors of light.
Check Your Understanding
1. Two lights are arranged above a white sheet of paper. When the lights are turned on they illuminate the entire sheet of paper (as seen in the diagram below). Each light bulb emits a primary color of light - red (R), green (G), and blue (
. Depending on which primary color of light is used, the paper will appear a different color. Express your understanding of color addition by determining the color which the sheet of paper will appear in the diagrams below.
Depress mouse to view answer.R + G ---> YellowR + B ---> MagentaB + G ---> Cyan
2. If magenta light and yellow light are added together, will white light be produced? Explain.
Depress mouse to view answer.No. Magenta is a combination of redand blue light and yellow is acombination of red and green light.(Note the double abundance of red.)Combining magenta and yellow willproduce a whitish-red color - thatis, pink.
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CONTINUED...
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