Mercury: A Broader Perspective
Mercury: A Broader Perspective
Although most lamps contain mercury, efficient lighting reduces the mercury (and other pollution) released by electric power plants. Meanwhile, recovery/reuse efforts and legislation on lamp disposal are becoming important parts of the lighting landscape.
When bathed in an electric current, excited mercury atoms in fluorescent lamps emit invisible UV radiation, which is quickly absorbed by phosphors located on the lamp wall. The happy phosphors then re-radiate visible light. Mercury vapor, metal halide, and high-pressure sodium lamps also contain mercury.
Mercury is a toxic heavy metal and bioaccumulator, and in sufficient doses it can cause damage to the central nervous system, birth defects, and other adverse health effects. Concerns are often raised about the mercury in compact fluorescent lamps. Perhaps this is because CFLs are marketed as a replacement for incandescent lamps, which do not contain mercury.
However, other discharge lamps contain significantly more mercury per lamp and more mercury on an aggregate national scale. For example, the mercury in CFLs sold in Europe represents five percent of the mercury from all lamps (the main source is long fluorescent tubes). According to the European Lighting Council, mercury from all lamps represents 0.2% (5.2 tonnes/year) of the mercury contained in consumer products sold in Europe.
The trend is towards less mercury per lamp. The quantities used in long fluorescent tubes, for example, have fallen by a factor of two to three in recent decades. The US National Equipment Manufacturers Association projects a further 35% reduction for T12 (1.5-inch) lamps between 1990 and 1995. An analysis from Chalmers University in Sweden shows that total lamp-related quantities of mercury continue to decline even as the number of lamps sold increases. Emerging lamp technologies may eliminate mercury altogether, without sacrificing efficiency.
A SYSTEMS VIEW
The relationship between mercury levels and lamp energy-efficiency shows why the "systems" nature of lighting is important.
Lamps can be compared on the basis of mercury per unit of light produced. By this measure, longer-lived lamps result in lower annual flows of lamp-related mercury into the environment. Where mercury-containing fossil fuel is used, as shown in the diagram, increased lighting efficacy is also consistent with reducing mercury flows. For example, based on the US fuel mix for electricity production, the mercury releases from operating incandescent lamps are three-times greater than for CFLs.
The amount of mercury present in the emissions from a utility system depends on power plant efficiency and fuel mix. Efficient lighting can also reduce the generation of nuclear waste (representing other objectionable heavy metals), greenhouse-gas emissions, and other effects of power production-not to mention the cost of providing illumination.
Mercury releases associated with power production are not well understood. Coal contains more than other fossil fuels, but exact concentrations vary wildly, especially when fuel-cycle releases are considered (for example, mercury often condenses in natural gas pipelines). The mercury content in US coal has been found to vary from 0.01 to 8 ppmw.
Using the German value of 0.1 ppm, a large 1 000 megawatt coal-fired power plant produces 150 kilograms of mercury each year. This mercury is distributed between airborne emissions and ash, depending on the type of stack-cleaning equipment.
The ultimate pathways of human exposure to mercury and its environmental impacts depend on the methylation of released mercury, leaching and vaporization of solid mercury waste during transport and from landfills, emissions control devices used in power plants or waste incinerators, atmospheric residence times and deposition of airborne emissions, and worker environment (lamp assembly and disposal-in Sweden CFLs are disassembled by hand!).
The greatest opportunity to control lamp-related human exposure happens during collection, transport, reprocessing, and disposal. Inserting old lamps in boxes helps avoid breakage. If reprocessing is unavailable, sealing lamps in plastic bags (perhaps with a few eggshells-they are sulfurous-to bind with any free mercury) reduces the risk of worker exposure resulting from breakage. (Continue to "Mercury and Lighting: Managing the Problem, IAEEL 3/93)
Evan Mills
| All fossil fuels contain mercury. Based on the US fuel mix for electricity production (56% coal, 9% natural gas, 4% oil, and 31% non-fossil fuels) the mercury releases from operating incandescent lamps are three-times greater than for CFLs. |
| Incandescent (60W, 0 mg Hg) |
| Halogen (90W, 0 mg Hg) |
| Mercury vapor (450W, 75 mg Hg) |
| CFL (15W, 5 mg Hg) |
| 2-lamp 40W fluorescent (95W, 40 mg Hg*) |
| Metal halide (450, 60 mg Hg) |
| 2-lamp 32W fluorescent (65W, 30 mg Hg*) |
| High-pressure sodium (475W, 20 mg Hg) |
| Low-pressure sodium (215W, 0 mg Hg) |
| (*Mercury in each lamp) |
| The total amount of mercury in lamps in Sweden has decreased even though the number of lamps sold has increased. |