How much mercury do compact fluorescent lights contain?

According to the United States Environmental Protection Agency CFLs contain around 4mg of mercury. By comparison, older household thermostats contain about 750 times as much, so 4mg is not much in comparison to other mercury-containing household items but mercury is bad stuff in any concentration. While incandescent and LED lights may contain minuscule amounts of mercury in their solder, it is negligible in comparison. So, if you were looking strictly at the manufacture of the bulbs, you would certainly want to stick with the incandescent, or the more costly LEDs, which have about the same energy efficiency benefits as CFLs without the mercury.  

Why do compact fluorescent lights even contain mercury?

When an electrical current is applied to mercury it turns from a liquid to a gas and emits a specific range of ultra violet (UV) light. This UV light causes the phosphor coating on the inside of the glass to glow, or fluoresce, creating useful light.  

So Why would I want to use compact fluorescent lights?

Both bulbs require electricity. An incandescent bulb requires about 4x more energy to provide the same amount of light. You may or may not be surprised that 40% of US mercury emissions come from coal-fired power plants and 65% of mercury emissions come from the combustion of all fossil fuels. In contrast, only about 3% of mercury emissions come from waste disposal, which may sadly include the improper disposal of CFLs (For more information on the proper disposal of CFLs click here).

What's the bottom line on compact fluorescent lights?

Over 5 years (the life of a CFL) it may be responsible for 2.4mg of smokestack mercury emissions, so a total of 6.4mg of mercury over the life of the bulb. By comparison the incandescent bulb is responsible for almost 10mg of mercury emissions over 5 years. But CFLs can be recycled to recapture the mercury. Smokestack emissions can not be recaptured after they enter the atmosphere.

Ask Pablo is a weekly column that aims to answer your pressing eco-quandries. Want to ask Pablo a question? Simply email Pablo(at)treehugger(dot)com. Wondering why Pablo's qualified to answer? As the Vice President of Greenhouse Gas Management at ClimateCHECK, he helps major corporations measure and manage their greenhouse gas emissions.

Additional Resources on Compact Fluorescent Lights
Ask TreeHugger: Is Mercury from a Broken CFL Dangerous?
Should I Switch to Dimmable CFL Bulbs?

Further Resources on Compact Fluorescent Lights
CFLs Have One Hitch: Toxic Mercury
Mercury Fear on CFL Bulbs Overblown?