There are three primary types of bulbs in use today: incandescent, compact fluorescent lamps (CFL) and tubular fluorescent, and Light Emitting Diode (LED) bulbs.
Of these varieties, CFL and fluorescent tubes pose the most harm to the environment because they contain a small amount of mercury. Also known as a mercury-vapor lamp, fluorescent lamps discharge gas and product light when an electric arc courses through the vaporized mercury. While LED lights may not contain mercury, they may contain small amounts of lead and other metals, and significant amounts of plastics and electronics that should be kept out of the landfill.
Most curbside recyclers will not accept CFL and fluorescent bulbs, however they are recyclable, and it only requires a little extra effort to spare the environment from mercury contamination and make the material resources available for reuse.  Read our blog on CFL recycling to learn more about identifying and properly disposing of fluorescent bulbs.