In this activity, students use a handheld (tube) spectroscope to view different light sources, then on their lab papers, show which portion(s) of the visible spectrum are not emitted from the light.
I use this in conjunction with my light demos (free, in my store).
I also included an idea for an alternative activity, which I have used with success a few times. In this activity, rather than focus on how different light emit different parts of the spectrum, we look at why certain objects look certain colors, by using the spectroscope to see which colors REFLECT off various objects.
I have read that some teachers have problems with spectroscope use, but I've used the tube kind, seen here (http://www.enasco.com/product/SB11146M) <--Enasco "spectroscope kit" with great success with my 7th graders. Over the years, I've just purchased replacement diffraction grating to refresh some of the older ones (the spectrum will fade as the grating ages).
These activities could easily be used, or tweaked, to work all the way through high school.
Time: 30-50 minutes
Materials: Three different light sources (or use alternative lab), spectroscopes