Complimentary Teacher Lesson Plan
Diffraction Grating – The Study of Color & Light
Objective: To gain an understanding of where colors originate (in light); how the colors of the rainbow combine to create the various colors (including white light); how color filters affect various colors.
Materials: 1) overhead projector and three (to adequately cover) half-sheets of black construction paper (4-1/4" by 11")
and a clear plastic photo display holder with foot to hang
over the top edge of the projection lens of the overhead projector
3) diffraction grating glasses (Rainbow Symphony)
4) colored gels or filter materials (available from science
supply houses such as)
5) clear light bulb (40 watt (cooler) preferably, but not
absolutely necessary); green, blue and red 25 party
light bulbs; inexpensive bug light; a small 3.5 watt
(or nearly so) fluorescent night light, easily obtained
at super drug stores or hardware stores
Procedure: 1a) Use the overhead projector about 1/2 the distance
from the screen as is normal for projecting images; the spectra (rainbows)
are on either side of the projection window...
Project the white light on the screen and discuss the
makeup of the light... Use the diffraction
grating (4" by 4") mounted (in plastic photo frame with
foot to hang on projection lens, if you have it) to hold it
flat over the lens, and note the wash of light into a
suggestion of colors (on the sides of the projection window
primarily); ask where this suggestion of color is
coming from... Then while the students are watching,
place the three half-sheets of black construction paper
over the projection table so as to allow only light from a
strip about 1 cm wide to pass through; note the exquisite
definition of the colors of the rainbow on either
side of the narrow slot of dimmer white light...
A discussion of Newton’s discovery of passing a sample of
light through such a mechanism could be appropriate for higher
grade levels... Again discuss where the light is coming from...
A discussion of diffraction versus refraction might be appropriate
for higher grade levels...
Discussion: the various colors of the spectra are the slot of light
reproduced in the different energies (colors) and overlapping as
they blend from one to the next; each energy (color) bends
through the diffraction grating at different angles
(Note: the amount of bending from the central slot of light
is reverse order (red to violet) with a prism; an interesting
difference between diffraction and refraction)
1b) Use colored gels laid across the narrow slot to see the
effect of the various color filters on the light coming
through the slot (called a slit in a professional spectrograph)
and discuss what is happening to change the projected colors...
2) Use the diffraction grating glasses, one to a student,
to do the following; stress that the glasses represent a
light analysis tool and that scientists use basically the
same kind of tool, only much more sophisticated...
1) look at light from ceiling fixtures (they will anyway)
and light coming in through the windows; note that the light has the
same washed out appearance as the diffraction grating over the
projection lens of an overhead projector...
2) in a room darkened substantially, view the light of
a clear light bulb, with and without the light analyzers;
make a log of this on a log sheet
3) look at the light of a small fluorescent night light in
the same way as in 2; note that the shape of the
night light is nearly an elongated slot
4) look at the light of the colored light bulbs as in 2
5) look at the light of the inexpensive bug light as in
2; note that the spectra is easily seen to be different;
(note that what scientists do is to see these differences
in great detail and to understand what causes the differences, such as
composition and temperature of source and filter
Rainbow Symphony Inc.
6860 Canby Ave. #120
Reseda, CA 91335
Tel: (818) 708-8400
Fax: (818) 708-8470
Toll Free: (800) 821-5122
GEMS/Lawrence Hall of Science
University of California
Berkeley, CA 94720
About 300 years ago, Sir Issac Newton saw a beam of sunlight through a glass prism. He discovered that light is made up of a spectrum of seven distinct visible colors. This spectrum of colors always appears in the same order. You can see this color spectrum (Red, Orange, Yellow, Green, Blue, Indigo, Violet and all the colors in between) when you look through your Rainbow Symphony Diffraction Grating Glasses. There are two color ranges that are not visible to our eyes in this spectrum: below red is infra-red and above violet is ultra-violet. In a rainbow after a rainstorm this same color spectrum appears in the same order. Rainbows are created when sunlight passes through rain drops that act as millions of tiny prisms.
The color of a solid object depends on the colors of light that it reflects. A red object looks red because it reflects red light and absorbs all other colors. A blue object looks blue because it reflects blue light and absorbs all other colors. A white object reflects all colors of light equally and appears white. A black object absorbs all colors and reflects no visible light and appears black. Just like when you color with too many colors in one area with crayons or markers, all colors are absorbed, none are reflected and it appears black!
NEVER look directly at the sun because it could damage your eyes.
©2007 Rainbow Symphony, Inc.