$5 color meter
 

Years ago I used a large spectroscope to photograph a hydrogen spectrum with the goal of resolving the hydrogen-deuterium line separation for a school physics project. Recently I picked up a smaller spectroscope useful for analyzing potential light sources. It's a little plastic device with a diffraction grating and a slit on one end. You sight through the device at your light source and look over to the side to see the spectral composition of your source. For instance a tungsten source shows a smooth spectrum from deep red to violet, a fluorescent tube shows red, blue, and green bands. An LED source shows the expected cutoff at the deep blue region. Although they claim it's a quantitative device I don't think it gives you much more than a qualitative comparison of sources. About $5. EISCO Premium Quantitative Spectroscope, +/- 5nm Accuracy: Science Lab Spectrometers: Amazon.com: Industrial & Scientific

Re: $5 color meter
 

I remember one of those from the Open University science foundation course.