Make a spectroscope You get good spectrum outside at night because the light is
coming from one definite direction -- a light that is
small or far away -- and in other directions
there is just darkness against which to see the spectrum.
You get poor effects inside with all the lights on because the
spectrum of each part of each of the lights is overlapping the
spectra of other parts of other lights.
We can see good spectra without having to go outside at night, by
making a spectroscope. By only letting light in through a
slit, we eliminate the confusion caused by other lights; and
by looking into a closed box, we get darkness.
So, go make one!
You will find more detailed
instructions in the manual (Colors #3).
Compare what you can see looking at the fluorescent lights
in your school using the spectroscope and just using a
diffraction grating. The bright green and orange are the
clue that there is a mercury discharge light inside; the
white light that makes all the other colors is due to special
chemicals which convert ultraviolet light (that we can't see)
into visible light.
If you made a relatively wide slit, you will get a nice bright
spectrum, but you might miss some details. Using the most narrow slit
you can make, try looking at a cloud
(Don't look at the sun!).
You may see some dark lines in the spectrum, representing wavelengths
that are missing because they are absorbed in the atmosphere of the
sun.
You can compare the spectra you see indoors and out with a
page of photographs
Look at the differently colored panels
on the next page using the spectroscope.