Compact fluorescent light bulbs (CFLs) are gaining in popularity as countries around the world enact legislation to phase out incandescent light bulbs. CFLs are reported to use 2-5 times less power and last 8-10 times longer than traditional incandescent bulbs.  Since lighting consumes an estimated 19% of global electricity and replacing light bulbs is a relatively easy task compared to other energy saving measures, such as insulating buildings or replacing inefficient water heaters, it is considered a low effort method to reduce overall global energy consumption. 
In traditional incandescent light bulbs electric current is passed through a wire filament until the heat from the electrical resistance causes the filament to glow. This is a relatively inefficient way of producing light because a large amount of the energy is lost due to heat. CFL bulbs, on the other hand, produce ultraviolet light when an electric current is passed through a tube that contains argon and a small amount of mercury. This ultraviolet light is converted to visible light by exciting a fluorescent coating on the tube. Overall, less energy is lost through heat, making CFLs more energy efficient.
According to a 2011 report in Renewable and Sustainable Energy Reviews, in 2007 China produced 80% of the world market of CFLs (3.0 billion CFL bulbs). While it is not surprising that China has such a dominant role in the manufacturing of CFL bulbs due to lower labor costs, it should be pointed out that CFL manufacturing in the US and Europe is restricted due to stricter environmental and worker health and safety laws. This has raised questions about the local environmental effects of CFL manufacturing and exposure levels of mercury to factory workers.
In order for CFLs to reach US consumers, the bulbs are tested for quality to ensure that they meet energy standards. While the pass rate for large manufacturers is 100%, it drops to 62.5% for medium size manufacturers and 50% for small manufacturers.  It is unclear what happens to these defective bulbs, however, if they are sold and used in large quantities then overall global energy savings from CFLs could be lower than expected. Even if these defective CFLs are not used, they still must be disposed of. While the amount of mercury in each CFL bulb is quite low, disposing of large amounts of CFLs improperly can contaminate the local environment.
One of the greatest concerns of CFL use is the risk associated with exposure to mercury contained within the bulb. It has been demonstrated that the switch to CFLs results in a lower global release of mercury into the environment: 10mg of mercury to produce the electricity for an incandescent versus 2.4 mg of mercury present in a CFL bulb.  However, immediate exposure to mercury from a broken bulb could present some level of health risk since mercury gas concentrations in the vicinity of a broken bulb can be 2-8 times higher than the average 8-hour occupational exposure limit allowed by US health regulations. 
There is limited information on the health effects of incidental exposure to mercury from CFL bulbs. Mercury is well known for its toxicity to humans, effecting the central nervous system and negatively impacting neural development in children. Humans are exposed to environmental mercury on a daily basis through mercury emissions from power plants and consumption of fish. Absorption of mercury from a broken CFL can vary greatly depending on how well a room is ventilated, as well as clean up methods of the surrounding area. Furthermore, the effects of mercury absorption can vary greatly between people of different age, weight, and tolerance. To keep the amount of mercury present in a CFL bulb in perspective with other common sources of mercury, consider that a typical mercury thermometer contains 500mg of mercury versus 3-5mg per CFL light bulb.  This comparison should not be interpreted as a conclusion that the amount of mercury contained within a CFL is harmless; the intention is to give readers a relative understanding of mercury quantities that may be familiar. It is important to remember that replacement of mercury containing thermometers has played an important role in limiting mercury exposure to humans.
Due to concerns over mercury exposure as well as the perceived lower quality of light emitted from CFLs, the Department of Energy sponsored the Bright Tomorrow Lighting Prize (L Prize) competition to spur innovation in developing a superior bulb. Philips Lighting North America was named as the first winner for a highly efficient light emitting diode (LED) type bulb.  Although this winning bulb is said to meet very high standards of performance, quality, lifetime, cost, and feasibility for widespread adoption, it remains to be seen if consumers and manufacturers will adopt this over CFL technology as a new standard for lighting.
© Clara Druzgalski. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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