Fingerprints for light sources.

Using a diffraction grating, you can observe that what seems to be a single color of light may really be a combination of colors, called a spectrum. You can also compare the spectra produced by different light sources.

A shoe box or a [...]

Some light sources may appear to wiggle and flash when you give them the raspberry, but the only thing wiggling is you

Some light sources flash on and off many times a second. When you give them the “Bronx cheer,” you can see the their hidden flickering. [...]