Lighting and Mercury: Facts Support Choice of CFLs
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by Richard Reis, P.E |
Back-of-the-envelope calculations address the question of environmental and cost tradeoffs in using lamps that contain mercury versus using less efficient conventional lamps
In speaking with other attendees at the recent Takoma Park Green Building Conference and other similar events, I heard some confusion about whether using a compact fluorescent lamp (CFL) is really good for the environment, considering that it contains mercury. One person said that a CFL contains only 3 micrograms of mercury. At some booths, I was told that CFL lighting was irrelevant, as light-emitting diode (LED) lighting is available, more efficient, and cost-effective. Another person said that efficiency does not matter because solar cells can provide ample power at lower costs. (Contact the author for articles about lighting technology and efficiency versus alternative energy.)
The back-of-the-envelope calculations in this article address the question: What are the environmental and cost tradeoffs in using lamps that contain mercury compared with using conventional lamps that are much less efficient? (I call these calculations back of the envelope because they are based upon limited data and are approximate.)
Many types of lamps, particularly efficient lamps, contain mercury. This article will focus on CFL lighting.
To assess the impact, consider the following factors:
1. When any lamp is properly disposed, the mercury is recovered and not discharged into the air, land, or water.
2. The electric-generating stations emit mercury as well as other pollutants in proportion to power demand.
3. Conventional (incandescent) lamps demand more power than CFLs.
How does mercury harm humans?
The National Institutes of Health1 (NIH) state the following: Elemental (metallic) mercury and all of its compounds are toxic, exposure to excessive levels can permanently damage or fatally injure the brain and kidneys. This NIH web site article describes the life cycle through which mercury emitted by burning coal can accumulate as it travels up the food chain and becomes part of the food we eat.
How much mercury is emitted per unit of electric energy?
Wisconsin, like the Mid-Atlantic region, relies most heavily on coal-fired electricity generation, except during rare summer peaks. In a report2 for the State of Wisconsin, Table 1-3 shows emissions of about 0.05 pounds of mercury per gigawatt hours (GWh) (1,000,000 kilowatt hours [kWh]). Using common conversion tables, this is equivalent to 0.023 milligram (mg) per kWh. This electrical generation also produces other pollution such as oxides of sulfur and nitrogen and global-warming gases. A coal-fired generating station emits about two pounds of carbon dioxide (CO2), the most common global-warming gas, for each kWh of electricity. We can also choose higher-cost electricity produced from alternative energy, such as wind.
How much mercury do CFLs and conventional lamps contain?
In an article entitled Mercury Use in Lighting,3 Table 2 shows that 66 percent of CFLs contain 0 to 5 mg of mercury, 30 percent contain between 5 and 10 mg, and 4 percent contain between 10 and 50 mg. Assuming that each lamp in its cluster has the middle level of mercury, the level computes to 5.1 mg of mercury.
The two examples below provide a comparison between a CFL and a conventional lamp. (An mg is 1/1000 of a gram. A microgram is 1/1000 of an mg.
Ten 100-watt conventional lamps have a lifetime equal to one CFL.
Each conventional incandescent lamp lasts 1,000 hours. The 10 lamps then consume 1,000 kWh (100w x 10,000 hours) over their lifetimes. To supply these lamps, power plants will emit about 23 mg of mercury and 2,000 pounds of CO2. A consumer will spend $5 to buy these lamps (50¢ each) and $100 in energy costs to power them at 10¢ per kWh for a total of $105. The light output is 1,500 lumens or about 15 lumens per watt. Note: Conventional bulbs may contain lead solder, and lead is a powerful toxin as well.
One 23-watt CFL has the equivalent output of a 100-watt incandescent lamp.
The lamp lasts 10,000 hours and consumes 230 kWh over its lifetime. To supply that lamp, power plants will emit about 5.2 mg of mercury and about 460 pounds of CO2. Improper disposal of the lamp (for example, if it is consumed in a municipal incinerator) will result in 5.1 mg of mercury entering the environment. In this case the total emissions will be 10.3 mg mercury or about half of the emissions using conventional lamps. However, most jurisdictions provide facilities that allow residents to responsibly dispose of CFLs and other hazardous waste.
For example, Montgomery County residents can dispose of CFLs at its transfer station and at special hazardous waste collection events. The City of Takoma Park accepts used CFLs at its public works building on Oswego Avenue during business hours and in a drop box at other times. Ikea stores have recycling stations that accept light bulbs, batteries, and plastic bags. (You can find out more about lamp recycling at Earth911.org and LampRecycle.org.) One can buy these lamps at Home Depot and other places for $2.50 each and spend $23 (again at 10¢ per kWh) to power thema total cost of just $25.50 versus $105 using conventional lamps. The light output is 1,500 lumens or 65 lumens/ watt.
Light-emitting diode (LED) lighting has a bright future, but may not be ready for prime time for most applications. I found it difficult to obtain comparable data on available LED lamps in lumen output. However, Lighting Science sells a flame-tip lamp for $16.95, which emits a warm-white glow of 25 lumens and uses 1.2 watts or about 20 lumens per watt. We would need 60 lamps to match the lighting output of a single 100-watt incandescent or 23-watt CFL. Reports from Sandia National Laboratories4 and the Lighting Research Center5 predict significant progress in solid-state lighting in light output and lighting efficiency. It is also worth noting that LED lamps last 5 to 10 times longer than CFLs and 50 to 100 times longer than incandescent lamps.
Other Lighting Resources
Lighting vendors are beginning to address the need for sustainable lighting solutions. For example, Philips developed a web page6 that can help assess a Sustainable Lighting Index.
Summary and Action Step
CFL lighting results in less mercury and other pollution than conventional lighting even if these lamps are not disposed of correctly. Of course, it is far better to responsibly dispose of these lamps. Efficient lighting is a very cost-effective way to reduce pollution while saving money. The fact that monetary and environmental costs of electricity far outweigh the costs of the lamps themselves overrules the ethic of not discarding anything that is working; one should replace conventional lamps immediately.
Richard Reis, P.E. is a consulting engineer. He can be contacted at 301-384-0540 or firstname.lastname@example.org.
1 NIH Office of Research Facilities, http://orf.od.nih.gov, search mercury hazards
2 Focus on Energy Public Benefits Evaluation Estimating Seasonal and Peak Environmental Emissions FactorsFinal Report May 21, 2004 Evaluation Contractor: PA Government Services Inc.
3 "Mercury in Lighting" www.newmoa.org/prevention/mercury/imerc/factsheets/lighting.pdf, Northeast Waste Manage Officials Association
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