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Incandescent / Battle of the Bulbs
An Analysis
By Casey McCullough
Bellarmine College Preparatory /
Fluorescent

Compact fluorescent bulbs have proven an incredibly easy (and therefore incredibly popular) means of reducing one’s impact on the environment. They provide the same light as a traditional incandescent bulb while using approximately 25 percent of the energy. This has obvious and significant benefits in terms of reductions of greenhouse gases and other harmful forms of air emissions.

However, unbeknownst to most Americans, CFLs contain mercury, a toxic heavy metal. Though it is a relatively small amount (4 mg per bulb)[1], the growing number of these bulbs makes their use a real concern. If not disposed of properly, that mercury can enter ground or surface water and eventually biologic systems. Has the widespread transition from one type of bulb to another, have we traded in one environmental problem to solve another?

The question becomes more complicated when you realize that one of the other leading ways that mercury enters the environment is through the combustion of coal. Since coalfuels more electricity generation than any other energy source (both in the U.S. and the world, this becomes an important issue. The greater efficiency of CFLs clearly results in reduced consumption of coal and a corresponding reduction in mercury emissions.

So, the question posed to you is this: if we were solely concerned with reducing mercury emissions (outlandish) AND we assumed that everyone simply throws away their CFLs rather than disposing of them appropriately (perhaps not so outlandish), which bulb results in a greater release of mercury to the environment?

Step One: Using the table to the right, calculate how many kilowatt-hours of electricity is consumed by each bulb over a period of 6000 hours of use, the average lifespan of a CFL bulb[2]. /
Type of Bulb /
Incandescent /
Fluorescent
Power Used
(Watts) / 60 / 13
Light Output
(Lumens) / 800 / 800
Lifetime (Hours) / 750-1,000 / 6,000-15,000
Lifecycle Cost* / $40 / $10
Source: Energy Star:

Step Two: Calculate total mercury emissions per kilowatt-hour for all electricity generation in the U.S. Get the figure for mercury releases to the atmosphere from the EPA’s Toxic Releases Inventory (2007). You’ll also need total electricity generation for that year, which you can get from the DOE’s Energy Information Administration.

Step Three: Use the results from Steps One and Two to calculate the total airborne emissions resulting from the use of CFLs and incandescent bulbs over a 6000 hour lifetime.

Step Four: Calculate and compare the total mercury released into the environment by each bulb, assuming that the CFL is discarded inappropriately. What do your results show you?

[1]4 mg figure from FACT SHEET: Mercury in Compact Fluorescent Lamps (

[2] 6000 hour figure is based on Energy Star minimum rating for CFLs. Though it’s irrelevant to this calculation, it’s worth noting that the average CFL is not only more efficient than the average incandescent, it’s also more durable. You’d need at least six incandescent bulbs to provide as many hours of service as one CFL. (