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Metamerism Experiments
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This experiment is courtesy of 
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Is Your Blue Really Blue?
[Metamerism]
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Developers:
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Donald C. Snyder, Jr.
South Philadelphia High School
Philadelphia, PA
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Dr. Alan D. Stein
Senior Scientist, Exploratory Research
Dr. Donna Wetzel
Senior Scientist, Modifiers Research Dept.
Rohm and Haas Company
Bristol, PA
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Grade
Level:
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6 to 9
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Discipline:
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Physical Science
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Objectives:
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To teach students some fundamentals
about color perception, and to explain the phenomenon called
"metamerism".
Students will learn the three basic
components of color perception: light source, illuminated
colored object, and the light detector.
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Background:
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As Chevreul stated in 1854, "The art
of the tapestry weaver is based upon the principle of mixing
colours, and on the principle of their simultaneuos
contrast".
It is a common, though sometimes an
unpleasant discovery, that colors appear identical under one
light source but fail to match under another. This may be
familiar to you from mixing paints [trying to match paints
during automobile repairs, coordinating clothes, etc.]. Why
is this so?
Observing color requires three things:
a source of light, a "colored" object that the light
illuminates, and a detector.
Common light sources include
fluorescent, incandescent, ultraviolet, and sunlight. These
different light source have different spectral
distributions. Spectral distribution is defined as the curve
that illustrates the intensity of light emitted by the
source at each wavelength.
Dyes and pigments create the color in
objects such as textiles, paints, etc. Different dyes and
pigments have different spectral reflectance curves. The
spectral reflectance curve shows the fraction of the light
reflected at each wavelength from the material. Color
perception is a combination of the spectral reflectance of
the dye or pigment, and the spectral distribution of the
light source.
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Metamerism:
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Two colored objects made from two different dyes or
pigments may look the same under one light source, but
different under another light source. This is what is known
as metamerism. Two different colors may appear to be exactly
matched simply because the combination of spectral
reflectance and source distribution is fortuitously matched!
However, this pair will not be a perfect color match when
viewed with another light source. The combination of
spectral reflectance with the spectral distribution of the
second light source will be different, thus the colors will
be perceived as mismatched. The pair of colors are said to
exhibit metamerism. Pairs of colored objects having the same
spectral reflectance curves and therefore the same color
perception for all light sources are nonmetameric and form
an invariant pair.
The final component necessary for color perception is a
detector.
The human eye has a thin membrane, the retina, which
contains the light sensitive cells. The retina has two major
components: the rods and cones. The cones are sensitive to
colors. There are three types of cones in the human eye,
each contains a different photopigment with peak response to
a particular part of the visible sprectrum. Thus, by
differential transmission of nerve impulses upon
stimulation, the cones are able to encode information about
the spectral content of the image so that the observer
experiences the sensation of color. Each individual has a
different spectral sensitivity.
There is only one practical method to detect metameric
matches - view the samples under more than one light source.
This is what the laboratory involves!
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Management
Tips:
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Use the Macbeth Daylighting Metamerism Test Kit #3 -- "Do
these colors match or mismatch?" obtained through:
Macbeth - A division of Kollmorgen Company
Little Britain Road
P. O. Box 230
Newburgh, New York 12550
1-800-431-4952
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Materials:
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Macbeth Daylighting Metamersim Test
Kit #3
incandescent bulb [light
source]
fluorescent bulb [light source]
ultraviolet bulb [light source]
ultraviolet safety glasses
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Vocabulary:
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graph
spectra
spectral reflectance
ultraviolet radiation
color
incandescent
fluorescent
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dye
colorant
pigment
light
spectrum
metamerism
invariant pair
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Procedure:
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- Students will work in groups of
four or five.
- Observe the Macbeth Daylighting
Card under classroom light. Record your
observations.
- Observe your Macbeth Daylighting
Card under an incandescent light source. Record your
observations.
- Place the card under a fluorescent
light source. Record your observations.
- Place the card under an
ultraviolet light source. Record your
observations.
- Hold the card under direct
sunlight and record your findings.
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Questions:
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- How do the samples on the card compare to each other
under different light sources?
- How can you detect a metameric match?
- How can this test kit aid in everyday situations?
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References:
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Principles of Color Technology; Second Edition, Fred W.
Bellmeyer. Jr. and Max Saltzman, A. Wiley - Interscience
Publications; John Wiley and Sons, New York, 1981.
The Photonics Dictionary, TM Book 4 39th International
Edition, 1993, Larien Publishing Company Inc., Pittsfield,
MA 01202-4949.
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This experiment is courtesy of 
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