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Chapter 27

Chapter 27. C o l o r. 1. SELECTIVE REFLECTION. Most objects "reflect" rather than emit light. The spring model of the atom works well in explaining reflection. Radiations that match the resonant frequencies of the atoms are absorbed.

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Chapter 27

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  1. Chapter 27 Color

  2. 1. SELECTIVE REFLECTION • Most objects "reflect" rather than emit light. • The spring model of the atom works well in explaining reflection. • Radiations that match the resonant frequencies of the atoms are absorbed. • Frequencies of the radiations on either side of the resonant frequencies are “reflected.”

  3. Objects can only reflect the light that is in the source illuminating the object. • Demo – Razorback Football in Cyan Light (Next Slide)

  4. 2. SELECTIVE TRANSMISSION • As light passes through materials some frequencies of light are removed (absorbed) while other frequencies are transmitted. • The degree of transmission depends on how transparent the material happens to be.

  5. Color filters are good examples of selective transmission. • Demo – Color Filters and White Light

  6. 3. MIXINGCOLOREDLIGHT • All visible frequencies make up white light. • Example: The sun emits all frequencies and its light is white. • (Actually it is slightly yellowish to us on Earth, which possibly explains why we are more sensitive to light in the middle of the spectrum.)

  7. RED, GREEN, andBLUE when added also produce white. • Demo - Color Addition and Colored Shadows • Color Addition Schematic • Red, green, and blue are called the additive primaries.

  8. Color Addition

  9. Through color addition you are able to see a wide range of colors from a color TV or color projector which actually only emit three different colors. These colors are red, green, and blue. They are called the additive primaries.

  10. Your vision system “adds” these together to see a single color from a single location illuminated by more than one color. You even see colors that don’t appear in the continuous emission spectrum of the sun. Red, green, and blue are used as the additive primaries because this set of three will produce the widest range of colors that you visually experience.

  11. On the next slide you will see what happens as you add colors to produce other colors.

  12. Colors in White Light White Red Green Blue You can see that these three add to give white. Yellow Note that yellow is the addition of red and green. Cyan Magenta Note that cyan is the addition of green and blue. Note that magenta is the addition of red and blue.

  13. Tosummarize,seecoloraddition circles on next slide.

  14. ColorAdditionCircles What you are about to see is what you would get with three partially overlapping spotlights reflecting off a white screen. Yellow Red Green Cyan Magenta Blue

  15. Complementary Colors • Any two colors that add to give white are said to be complementary colors. • Demo - Complementary Colors

  16. 4. MIXINGCOLOREDPIGMENTS • Subtractive primaries - YELLOW, CYAN, and MAGENTA • Example - Mixing paints, zip-lock sandwich bags, color printing • Demo - Color Subtraction • Overhead - Foretravel Advertisement

  17. Color Subtraction

  18. Through color subtraction you are able to see a variety of colors from printings, paintings, etc. If you have ever bought printer inks, you will notice that the ones used to provide a variety of colors in printing are yellow, cyan, and magenta. They are called the subtractive primaries.

  19. In subtraction, colors are eliminated by the absorption of colors that were in the original illuminating source. This particular set of three colors, yellow, cyan, and magenta, will produce the widest range of colors that you visually experience.

  20. On the next slide you will see what happens as you remove different colors from white light.

  21. White Blue Yellow Colors in White Light You get blue. Take away yellow and what is left?

  22. White Cyan Red Colors in White Light You get red. Take away cyan and what is left?

  23. White Green Magenta Colors in White Light You get green. Take away magenta and what is left?

  24. Tosummarize,seecolorsubtraction circles on next slide.

  25. ColorSubtractionCircles What you are about to see is what you would get with three partially overlapping transparencies on an overhead projector. Green Cyan Yellow Blue Red Magenta

  26. It should be noted from the previous that objects that reflect a particular color are themselves good absorbers of the complimentary color of that particular color. • For examples: • A red object is a good absorber of cyan and vice versa. • A blue object is a good absorber of yellow and vice versa. • A green object is a good absorber of magenta (blues and reds) and vice versa.

  27. 5. WHY THE SKY IS BLUE

  28. Just as resonating tuning forks scatter sound, so do particles in our atmosphere scatter light. • N2 and O2 scatter high frequencies which are near natural frequencies of N2 and O2. • (Natural frequencies are in the UV.) • This scattering produces the bluish sky. • The blue end of the spectrum is scattered ten times better that the red end.

  29. Top of Atmosphere Sun Blue in this direction Earth

  30. 6. WHY SUNSETS ARERED Sunset • If the atmosphere becomes thicker or the paths of light through the atmosphere become longer, more of the longer wavelengths of light will be scattered.

  31. Sun Sun Earth

  32. Demo - Blue Sky and Red Sunset • Because of scattering of blue light the sun appears more yellowish at noon than it really is.

  33. 7. WHY CLOUDS AREWHITE • Droplet size dictates which colors are scattered best. • Low frequencies scatter from larger particles. • High frequencies scatter from small particles.

  34. Electrons close to one another in a cluster vibrate together and in step, which results in a greater intensity of scattered light than from the same number of electrons vibrating separately. • Large drops absorb more and scatter less.

  35. 8. WHY WATER IS GREENISH BLUE • Water quite often looks bluish. • This is due to reflected “sky light.” • A white object looks greenish blue when viewed through deep water.

  36. Water is a strong absorber in IR and a little in red. • Remove some of the red and cyan is left. • Crabs and other sea creatures appear black in deep water.

  37. 9. COLOR VISION ANDCOLOR DEFICIENCY • Colorblindness (color deficiency) affects about 10% of population • Red-green is predominant • Yellow-blue - a few • Total – some • Colorblindness Tests – URL

  38. 10. AFTER IMAGES • Slides - After Images

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