What are CFL bulbs?

CFLs, or compact fluorescent lights, are an environmentally friendly alternative to incandescent light bulbs. Typically a CFL is powered by a ballast which sends current into the glass envelope filled with halogen gas. 'Halogen' is not actually a gas in itself but refers to a family of gasses that includes chlorine, bromine, astatine, fluorine, and iodine. As the electric current travels from the ballast into the envelope, the gas becomes exciting and emits photons. Interestingly, without the the white coating inside a CFL, known as a phosphor coating, you would not be able to see the light produced. It is only once the light passes through the phosphor coating that it becomes a wavelength visible to the human eye.