Fluorescent light bulbs contain mercury gas inside of a tube that is coated with a fluorescent material. Fluorescence is the process by which electrons in an atom absorb a shorter wavelength of light and emit a photon of a longer wavelength of light.

The mercury gas inside the bulb produces ultraviolet (UV) light when exposed to an electric current, and this UV light reacts with the fluorescent coating to produce visible light.

The distinct peaks in the spectra of fluorescent bulbs are a result of the specific emission wavelengths of the electrons. These peaks can be seen in the spectral plots shown in Figure 5-5 and Figure 5-6. This unique spectrum can make it more difficult to identify light generated from fluorescent tubes or compact fluorescent light (CFL) bulbs.