Question

Color Mixing Name ______________________ Objective: To reason through additive and subtractive color mixing… the superposition of colored lights, the selective absorption of color filters, and the selective reflectance of colored objects. Apparatus: Colored lights, color filters, and colored paper. Please use the common color letters as follows… red (R), green (G), blue (B), yellow (Y), turquoise or cyan (C), and light purple or magenta (M). Introduction: The wavelength of light determines its color. In fact, most color that we usually see is not determined by just one single wavelength but by a broad range of wavelengths. If you see light consisting of wavelengths between 600 and 700 nm you sense the color red. If the light consists of wavelengths between 500 and 600 nm you sense green, and if wavelengths are between 400 and 500 nm you sense blue. These three colors that divide the visible portion of the electromagnetic spectrum are called primary colors. Other colors that we sense consist of combinations of these colors, or combinations of different portions of the spectrum of wavelengths. We can create other colors by additively mixing blue, green, and red light. Additive color mixing occurs when we create light consisting of the sum of the spectra from two or more other colors. For example, we can create white light, consisting of all wavelengths from 400 to 700 nm, by adding B, G, and R light. We will represent color addition symbolically as follows... R + G + B = W We can also create different colors by subtractive color mixing. A color filter selectively absorbs certain wavelengths of light and transmits all others. A red filter, for example, absorbs B and G light, and passes or transmits only R light. If we shine white light through a Y filter, passing R and G light, and then through a M filter that passes R and B light, the color that is commonly passed through both filters is R. This is an example of color subtraction. Objects have color because they selectively reflect and absorb certain colors of light. A green leaf, for example, reflects G, but absorbs R and B. PART I Additive Color Mixing 1. After viewing the color mixing session, indicate the color perceived by additively superimposing these colored lights… a) G + R = b) B + R = c) B + G = d) R + G + B = 2. For each of the combinations below, predict what color will be created. Follow the example given, showing your work… a) R + C = R + (B + G) = W b) M + G = c) M + C = d) M + Y = e) C + Y = f) M + C + Y = g) Y + B = PART II Subtractive Color Mixing One way to produce subtractive color mixing is to place color filters back to back and either project white light through them onto a screen or look through them at a source of white light. For each of the combinations below predict what color will result. Give your reasoning, depending on what colors each filter absorbs or passes. I think it’s easiest to think of which colors are commonly passed by both filters. Be careful with the “– “ symbol… It is just an indication of color subtraction. Show your work, following my examples. a) M - Y = passes (B + R) – passes (G + R) = R (R is commonly passed) b) R - B = passes (R) – passes (B) = 0 (black) (no color is commonly passed, all light is absorbed) c) Y - C = d) C - M = e) M - G = f) R - Y = g) G - Y = h) C - B = i) G - B = PART III Selective Reflectance By illuminating colored paper with different colors of light, the paper may appear to be a different color, or black. Follow the combinations given below and make predictions of reflected color. This is similar to color filters in that the color your see is common to both that reflected by the paper and a component of the illuminating light. For each case, explain why you see that particular reflected color, following my example… Paper Color Color of Illuminating Light Apparent Color of Paper Y reflects (G + R) M = (B + R) R (both reflected and illuminated) R G R Y Y C C M B M G M These comments are not required These comments are not required

Answer 1

a) G + R = Y (since it is given that Y filter passes G and R implying red and green combine to form yellow)

b) B + R = M (similarly given that M filter passes blue and red implying that magenta is combined of red and blue)

c) B + G = C( therefore c must form from blue and green)

d) R + G + B =W (this is also given that red blue and green combine to form white)

2. For each of the combinations below, predict what color will be created.

Follow the example given, showing your work… a) R + C = R + (B + G) = W

b) M + G = (B+R)+G=W

c) M + C = (B+R)+(B+G) = W+B =B

d) M + Y = (B+R) +(G+R)= W+R=R

e) C + Y =(G+B)+(R+G)=W+G=G

f) M + C + Y =(B+R) +(B+G)+(R+G)=W+W=W

g) Y + B =(R+G)+B=W

PART II Subtractive Color Mixing

a) M - Y = passes (B + R) – passes (G + R) = R (R is commonly passed)

b) R - B = passes (R) – passes (B) = 0 (black) (no color is commonly passed, all light is absorbed)

c) Y - C =passes(R+G) -passes(B+G) = G

d) C - M = passes(B+G) -passes(B+R)=B

e) M - G = passes(B+R) -passes(G)=0(black)

f) R - Y = passes(R) -passes(R+G)=R

g) G - Y =passes(G)-passes(R+G)=G

h) C - B =passes(B+G) -passes(B)=B

i) G - B = passes(G) -passes(B)=0( black)

PART III Selective Reflectance

Paper Color Color of Illuminating Light Apparent Color of Paper

Y reflects (G + R)....................M = (B + R)........................... R (both reflected and illuminated)

R .............................................. G................................................ 0(BLACK)

R............................................ Y=(G+R).......................................R

Y (R+G) ..................................C=(B+G)......................................G

C(B+G).................................... M(R+B).......................................B

B...............................................M(B+R)........................................B

G.............................................. M(B+R).......................................0(black)